One thing I would do for your camera gear if you don't buy a specialty pack is go to a Target, Wal-Mart or Dick's and buy a blue foam sleeping pad and a can of neoprene or wesuit cement. These pads have been around for years and are often the first pad anyone buys. Should be around $10 at the most. They are dense closed cell foam about a half inch think and baby blue (usually). The cement (also called Barge cement which is a brand name), works well on it. A dive shop or place like Home Depot should have it since it can be used on foam insulation.

Use the foam to make dividers or lightweight padded cases for lenses or camera bodies. I've made an insulated case for a thermos bottle and a few other things with it.

On another note from your original post-leave the jeans at home. Once they get wet they are worse than useless and I mean that-heavy and with no insulation at all. Wet jeans can lead to hypothermia which can kill you. Not trying to be dramatic, but those are the facts. If you can't afford fancy hiking pants, don't worry, get a pair of cheap wool pants and wear those. Army surplus stores have them, so does Goodwill and stores like them. Forget anything made of cotton in cold weather unless you are in sub zero weather (I will skip why cotton works in really cold weather for the moment) and I mean anything including underwear. Get anything synthetic. Doesn't have to be fancy. Target and other discount stores carry a lot of synthetic stuff. Dick's should have some cheap snowboard pants and those will work too. Sierra Trading Post is a good place online to buy stuff at heavily discounted prices. I've bought a couple of things from them and they have great customer service if you have to return something.

I have some Patagonia Capilene base layer pieces. The prices are outrageous, but I have two pieces, a top and bottom I bought 25 years ago and they are still fine after quite a bit of wear. They have sales once in a while. Beware of fakes on eBay; there are a lot of TNF (North Face) counterfeit goods on the net, especially on eBay. I've even seen manufacturer's notices for fake climbing gear (Petzl).