"Backpacking (Ul or otherwise) is usually about staying on the trails and carrying everything you need to be safe for x amount of days and if you get in trouble be prepared to stay out a few days/nights until rescue or self rescue.
- bushcraft ( some people mistakenly call it survivalism )
is all about living of the land and stresses deep knowledge of the enviroment -botany,mycrology,ect. and bushcraft skills ,like making your shelter not carrying it ( well they might bring parts of it), finding and processing your food -plant and animal.
Some here might be suprised that when I took a coarse with Mors Kochanski that he said his pack weight was like 4-6 bls. and he stressed the idea that the more you know the less you carry."
I would add that there are some of us backpackers(UL, SUL, and otherwise) who do, in fact, spend quite a bit of time off trail, but who either don't want to kill for food and/or rip up the landscape to build shelter and fire, or backpack where it is prohibited in part or totally. Doesn't mean we don't understand our environment, just that we prefer to enjoy it as it is and leave it that way. In most cases, I would venture to say, we could probably figure out how to obtain enough food to survive and stay warm and dry if it became necessary. Just one more niche in the backpacking universe, I guess.