Summer time is gone, even here in sunny Kalifornia so it's time to re-think and re-pack your git kits. My pack is configured to keep me sustained for 3 days and that's food, medications, clothing, shelter, water purification, first aid, personal hygiene, a roll of 4 ply Charmin because I have a delicate heinie and other basic survival items.
Take out the summer clothing and the poncho liners and add the heavier clothing and sleeping bag. Throw in a couple of pairs of hunting gloves. Check your food and make sure you have enough additional calories for winter ops and kick in a few extra energy bars for good measure. Change out your matches and lighters, sunscreen, meds, and spare batteries. Inventory your first aid kit and throw in a couple of space blankets and lip balm. Don't forget the wool watchcaps, bacalavas and shemag rags. I hear that not only do they keep your head warm but they make pretty handy masks.
Another thing that I add is some of that firestarter made by Duraflame, found at your local market. Buy a brick of that and cut some pieces off and put them in baggies. No sense in carrying around the whole brick unless your firemaking skills are completely hopeless.
Once your pack is completely repacked, take it outside and waterproof the hell out of it, being sure to cover it thoroughly, every nook, cranny and wrinkle. I use Kiwi's Camp Dry for canvas, but the chemical smell is so bad it'll give you a headache unless you leave it outside overnight to air out. The stuff does work - just make sure you get the stuff for canvas and not cloth.
Don't neglect your footwear. You ain't gonna be effective if your feet are wet and so cold that you can't feel them, or so blistered and sore you wished you couldn't. Make sure you waterproof them, again with Kiwi's, paying particular attention to the seams and tongue. Replace the laces that came with them with 550 cord. Cut it to length, melt the ends shut and lace 'em in. I use 550 cord on my workboots and the boots wear out before the 550 cord even looks worn. Most of all, make sure your boots fit. Don't mail order them, go to the store and actually try them on before you buy them.
Check your firearms, clean them and oil them according to your winter climate. Yes, it does matter. Inspect your cleaning kits, making sure you have plenty of oil. Clean and oil your magazines. Check your ammo for corrosion, replace as necessary. Check your knives and multi-tools, sharpen or tighten up as needed and give them a very light coating of oil.
Colder weather can be miserable if you're not prepared for it, and if you're in a position that you're having to use your git kit, you don't need to be worrying about being cold and wet. An hour or two right now can prevent that.
Oh, one more tip: If you wear glasses like I do, put some antifog stuff on them. Ask your optometrist what he recommends.