It can often sound silly but before you even leave your house you need to be prepared for the weather in any condition the main one being the cold as you're not going to be shooting in the rain but it can get very fierce especially here in the UK. Some of this may seem self explanatory but the amount of times i've seen people come out not prepared for the worse and be begging to go home because they are too cold. Here are some essentials that I usually take out with me, some of them stay in the car but if you need them they are there.
Just as a bottom layer it's good to have thermal everything, pants, top, socks.
Rather than having many layers restricting your mobility this is nice and thin and keeps you warm.
It's good to be warm and protected, but is all about personal preference really, I prefer a good pair of jeans, thick enough not to rip right away, as you tend to do a lot of kneeling down and get what we call "Night Photographers Knee" any pair of trousers will wear thin over time and rip at the knees, something I sometimes do is wear brick layers knee pads, bought from local DIY store cheaply and they do a great job, not only do they save my jeans they also protect my knees from any harsh surfaces. Jeans are also quite warm giving some insulation and wind protection as well as protecting you from nettles, brambles or any rusty metal you may run in to. I wouldn't suggest jogging pants or thin trousers as they need to be durable.
Wear a T-shirt and a Jumper or Hooded Top on top of your thermals but then you need a decent coat, one that keeps in the warm and has good insulation, but is not too big so you can't move in it, a decent amount of pockets is also vital to hold your torches, flashguns and any other tools you will need to have close by, something with a hood is usually good, but again it's personal preference.
The difference a scarf makes, it's the one place your coat doesn't cover, makes a nice seal around your neck to help keep in the warm, also you can cover your mouth and nose with it as well if it's that cold. If you wear glasses then it's not that practical because they will fog up when you breath in to it.
A good hat will keep you warm all night long, I personally use a Russian Hat which I specially had imported for night photography, in winter it is the best thing, keeps me warm, flaps come down keep ears warm, even ties under your chin to keep your whole face warm, in the summer it's a bit too hot and a or a normal beenie would do the trick.
Now this is a tricky one, because most warm gloves are very thick and operating your camera with them on is like making a cup of tea with boxing gloves on. I managed to find some industrial freezer gloves used in the building industry, they are thin and light but very insulated. Or you can buy specially made photographers gloves that come with the finger and thumb cut off to operate your dials with.
A good pair of socks will save the whole night for you, once your feet go numb the night will become very unenjoyable and you will not be giving 100% and you will soon grow tired and bored of having cold feet and wish to go home, this will mean you are missing out on shooting and possibly miss out on some great photos, depending on how far you are from home this may be the only time you are here. Depending what footwear I am wearing I will wear different socks, firstly a thin pair, then a ticker pair, then a pair of boots or shoes, If I am wearing wellington boots then wellington socks which are a must. Also always carry spares because a lot of places I go to are wet and over grown.
A good pair of boots will save you a lot of pain for a start, and help to keep your feet warm and dry, I would suggest walking boots because you actually clock up a good few miles in one night. Also another thing to look in to is, steel toe caps and steel soles, this is mainly in abandoned places for things falling on your feet or worse treading on 6inch nails. A simple small piece of metal could save you a nasty trip to the hospital.
Always sounds funny when I suggest these, but wearing sweat bands, like the scarf adds a seal around your wrist stopping the cold getting in up your sleeves.
They come in every size and every colour and are not expensive, so there is no excuse not to
own a pair seen as there are some places that will ruin your shoes or boots, I would suggest insulated ones as they can be very cold. keep them in a bin bag in your car so not to wreck your carpets.
Reusable Hand Warmers
Not your regular bit of clothing, but these can be life savers on a cold night. A gel based hand warmer with a small metal switch embedded within the gel compound. Pressing the metal switch activates a chemical reaction in the warmer and the gel hardens and releases heat as it goes. This will last for about 30 minutes until the gel is fully hard the the heat starts to fade. To reuse the warmer you will need to boil it in hot water for 15 minutes, this will then create another reaction the liquifies the gel in the warmer, it can then be reused again and again in the same way. Seen as they only last for 30 minutes it's good to have enough to last you the whole night. These can be bought for your hands, down your socks or even for the soles of your shoes.
I never go anywhere without my P3 mask, It's always good to do your research about chemicals and asbestos that may be in abandoned places you come across, it's better to be safe than sorry. Just a quick lesson in Asbestos while i'm talking masks. There are 3 main types of asbestos - White, Blue and Brown. White is considered the safest asbestos but it is by no means safe it is just the least lethal. Luckily the most common type of asbestos which is mainly found in buildings is white asbestos, you still need to protect yourself against it though. The main problems asbestos can cause is Malignant Lung Cancer and Mesothelioma.You can be exposed to asbestos heavily and feel relatively fine for years because asbestos poisoning won't hit you for about 40 years but when it does you will know about it so it is vital you protect yourself while you can. Don't take my word for it though do your research before walking blindly in to these places not knowing your stuff.