When you are picking say 2 jackets out of 3, that is a "combination" because, it doesn't matter what order you pick the jackets in, the two jackets are still the two jackets (doesn't matter if one was picked first).
So the possibilities for jackets is 3C2 and this is typically something you can type in your calculator to determine. If not, you have to use the equation:
It turns out that 3C2 = 3. You can easily see this if you just label the jackets as A, B, C. The possible choices are AB, AC, and BC.
The number of possibilities for sleeping bags is 7C2 and the number of possibilities for packets of food is 12C9
Once you get each of those values, just multiply them together to get the total number of possibilities. So:
Total # of ways the trip can be outfitted = (3C2)•(7C2)•(12C9)