If you are serious about nature photography, it is essential to provide yourself with the right clothing and footwear. You don't need, in my opinion anyway, to kit yourself out like an army commando in full camouflage but it is sensible to be appropriately dressed and fully prepared for any eventuality and whatever the weather.
Firstly, the right footwear is absolutely essential - you need to ensure your feet are dry and comfortable at all times otherwise it is difficult to feel creative when you have blisters or wet socks! You will be plodging around in mud and wet sand, as well as long, wet grass so you want something to keep your feet dry. Wellies are not the answer though, unless you are going wading and then a pair of waders are more useful. You are likely to scramble up hillsides and across slippery rocks so something with good grip is needed as well as adequate, cushioned support around your ankles, to provide protection in case you twist an ankle if your foot slips between wet rocks.
After trying a few shoes, I finally invested in a pair of all leather Brasher boots - yes, they are more expensive but they are the most comfortable I have ever worn. I have walked through wet sand and mud, been out in pouring rain and walked through snow but I have never had wet feet whilst wearing them, neither have I ever suffered blisters. The padded ankle support was a little stiff initially but after wearing them in for a while it soon softened up.
You need good quality socks as well - I have several pairs of Bridgedale Light Hiking socks which again, are not cheap but they are a worthwhile expense. I have never had a blister whilst wearing these socks and I have walked for miles in them but this is also in part, due to the boots keeping my feet dry. A worthy combination in my view, and worth the investment - your feet will thank you!
When I first started getting into nature photography, I would never kneel down as it would make my trousers dirty and leave marks! I soon realised how silly that was - it is par for the course with nature photography! You also soon realise that jeans, when they get wet take ages to dry and also get very hot, that thin cotton trousers tear easily and get waterlogged when wet, so it is wise to choose the right type of trousers. Another important factor, easily overlooked, is that many materials simply make too much noise - they rustle when you walk which frightens away birds and other wildlife like deer or squirrels!
Eventually I bought a few pairs of Crag Hoppers, which are designed for ramblers and hikers. The material is Teflon and so repels water whilst deflecting the heat of the sun, remaining cool and comfortable to wear and most importantly, they don't rustle. Lots of pockets are perfect for holding spare memory cards, mobile phone, lens caps, filters, money and even Extenders or short lenses. Once again, it pays to get quality clothing which will last - I've worn these Crag Hoppers so many times and they have not worn, torn or come unstitched and have even kept me relatively dry in light showers. I have a couple of pair in dark khaki green and a couple in light beige which are ideal for summer.
Crag Hopper also make shirts which have the same properties as the trousers, only lighter in weight. They are comfortable to wear, even in the height of summer, keeping you cool. Importantly, the collar provides protection for your neck when wearing a camera or even carrying a bag, so you don't get a sore neck from the strap rubbing. There are also a couple of pockets, of which you can never have enough.
Waistcoat or Vest
I know many people hate them but I do have a vest, made by Country Innovations, that I wear both in the summer if it is too warm for a jacket and in the winter as a layer under my jacket. Lightweight, very versatile and again, lots of pockets in which to keep all sorts of things, it was designed by Bill Oddie for bird watchers so some thought has gone into the position and angle of the pockets, making it equally useful for photography. The collar also provides neck protection against a camera or bag strap. I was teased mercilessly by Andy Rouse for wearing one of these on one of his workshops a few years ago but I didn't care, and still don't - they are very practical and comfortable.
I have a few dark green Thinsular fleeces which I wear during cold autumn and winter days. These trap your body heat to keep you warm and if it is really cold, I also wear a t-shirt underneath or the vest on the top. I don't like bulky clothing so these are comfortable to wear and if it turns warmer you can easily shed a layer. I also have a Thinsular woolly hat and pair of matching gloves - not very fetching perhaps but they do keep you warm and if you are sitting in a hide for hours on end you will certainly be thankful you brought them! I keep them in my backpack during winter months and in the car at other times. The gloves are fingerless to allow easy use of camera buttons etc but have mittens which fasten to the back of the glove with Velcro, so that when your hands get really cold, you can pull the mitten part over your fingers and warm up a bit. There is even a little slit in the thumb to allow turning the thumbwheel on the camera.
A really good all weather jacket is essential - it must keep you dry and warm and give some wind protection at least. I have two jackets, both made by Regatta of which one is lightweight and light in colour with sleeves which can be unzipped so it can be worn sleeveless as a vest when it gets warm - the sleeves making excellent lens pouches when not in use! There is a hood zipped into the collar so in a sudden shower, you can at least get some basic protection.
The other I wear from autumn through to late spring, it is more substantial and water resistant - essential for the rain we get here in the northwest. Again, there is a hood which zips into the collar, the cuffs and neck also have Velcro to fasten them up and give valuable protection from the wind. There are thicker winter coats available but I chose mine to be fairly lightweight and therefore be more practical and comfortable to wear - I can always wear an extra layer underneath. Ample pockets with inside access mean mobile phone, ipod, spare memory cards, filters can all be stashed away and still be easy to access - important when it is raining heavily or your hands are very cold. I have also recently acquired a full wax jacket for those days when the rain is torrential - completely waterproof with very deep pockets and lined, it should keep me warm and dry in the worst weather. I just need a hat to go with it to keep my head dry.
I carry a pair of knee pads, which I bought in B&Q, in my backpack during winter so if I need to kneel on very wet ground it does at least help to keep my trousers dry - even if I do look a bit odd. In the car I keep a pair of waterproof over-trousers which I can take out with me, or put on, as required. These are useful when doing close-ups of fungi on a wet or cold Autumn day or for when the ground is really wet but I don't really like them as they can make you too hot and it is hard to find some which don't rustle whilst you are walking in the woods.
All of the above items of clothing are either khaki green, brown or beige in colour so that they blend into the foliage or countryside, making you less visible to wildlife. Bright colours are not recommended, as your subject will see you coming!
Another tip is to avoid wearing perfume or after-shave, or any scented deodorant, especially if you are planning a trip to the woods to photograph wildlife, as they will smell you long before you even see them! And you can forget make-up - mascara doesn't impress the wildlife and if it rains heavily, you end up looking like a panda anyway! ;) I always carry lip balm in my coat pocket in winter as it does help to give some protection against cold winds. Insect repellent is essential in early summer, especially when photographing anywhere near riverbanks and ponds - as long as its not the insects you are trying to photograph of course! Mosquito bites can be extremely painful so it is as well to be prepared.
Having driven home in bare feet or wet socks, been so wet the driver's seat stayed wet for several days, I try to avoid being caught out too often by the British weather. I now keep a spare pair of clean trousers and an old pair of trainers in the back of the car for emergencies and have been very glad of them on more than one occasion! It can be a little difficult when you are parked in a public place and the windows are steaming up as you try to remove a wet pair of trousers but that's what nature photography is all about. ;)
As you can see, nature photography is not just about what lens to buy, what settings to use and which bag to take. As important, or perhaps more so, is being appropriately and sensibly dressed for comfort and being prepared for almost anything.
Another tip is to keep some biscuits, bottles of water or some chocolate in the car for those occasions when you stay out longer than planned and get very cold or wet! A flask of coffee is even better. Sandwiches take up little room in a backpack, and if you squeeze a bag of nuts in somewhere they also come in handy for attracting squirrels. Always keep your mobile phone handy as well, just in case you get stuck somewhere... literally.