I agree that caching is the only way to go if you seriously want to survive a winter away from home base. As you mentioned, one issue is food availability, but another serious concern is winter weather, so the ability to construct a meaningful shelter that you can heat with wood is imperative, at least in northern climates. I have done a fair amount of winter camping in Colorado, but I can tell you from experience that without meticulous attention to detail, anything more than a week and your gear needs to go inside to dry out. The primary problem is sweating into your sleeping bag and that water vapor freezing in the insulating material. After three or four days you are unable to actually repack a sleeping bag into your stuff sack and they loose their loft and ability to keep you warm. Your need a space you can heat!
I've put together quite an extensive list of what I'd cache, but it would take about six 55 gallon salvage drums to contain it all. Why so much? Well, first off, I need to build a rocket mass heater so I can have a smoke-free, highly efficient heat source. I also need durable winter gear. This is no place for fragile puffy down jackets or ultralight goretex; I want wool and fleece clothing that will hold up over time. I also need at least 250 pounds of food along with seeds to I can produce food efficiently in the future.
I'd focus on stuff with very good shelf life:
Rice, beans, salt, sugar, oats, corn, lentils, peas-- all of these items have shelf lives of a decade or longer, probably a lot longer if they're climate controlled and in the ground (where they'll never get over 55-60F).
Pasta, vitamins, protein powders, dry milk, dry eggs, dried meats, canned bacon, etc.-- These items are definitely good for 3-5 years, but do expect some deterioration after a decade. That doesn't mean they'll become bacterially compromised, but the proteins do break down over time, the fats will oxidize over time, and you'll lose a lot of nutrient value.
Oils--Definitely essential to life, definitely a very short shelf life for caching. Some things like olive oil might give you three years reliably if stored in a metal can under ideal conditions, but it's definitely an item that you'll want to swap out frequently.
Finally, one thing to consider is winter access. You'd be amazed at just how hard it is to dig something out that is buried 2-3' down in the middle of winter. Where I live, the frost line can go over 3'. That said, the right tools (I recommend a pick mattox) and the judicious use of fire over the cache over the period of hours or days will likely make the job a lot easier. Not having tried this, this is purely hypothetical.
Good luck!
