If you're looking for calories in a survival situation, I'd go for cambium long before I'd bother trying to set up snares (though I will admit my skills in that area are extremely limited).

Cambium (the layer between the wood and the bark in a tree) has lots of nutritional value, is everywhere, is easy to harvest (especially if you have a knife), and doesn't taste awful. It had been a staple food for native North Americans long before the white man came. (FWIW "Adirondack" means "bark-eater" in Iroquois, though in a derogatory sense). I was taught to go for birch or aspen, but I understand most species are quite satisfactory (eg white pine).

All that being said, food-gathering would be rather low on my list of priorities for a Altoid-tin-sized ditch kit. I would see hypothermia and first aid issues as much more serious risks, and would allocate my space accordingly.