Many human-edible seeds and nuts are relished by hermit crabs. These are a great source of protein and omega fatty acids.
Beechnuts--(see comment by Jedediah).
Coconut--a hermit crab favorite, probably abundant in their natural habitat. The husk is also readily eaten.
Walnut--a favorite food in my crabitat. I also feed the papery "guts" of the walnut shell.
Sunflower seed--well-liked food. I am not sure whether they eat the shell or not.
Pumpkin seed--actually, most squash seeds are safe.
Melon seeds are best avoided since many of them have toxic components.
Papaya seeds are best avoided, although I would like to work up the courage to do a food trial on them since the ones stored in my basement (I mean to make houseplants of them) attracted mice.
Peanuts, pecans, Brazil nuts (even the rancid ones) are all eaten safely by crabs.
Grass seeds and grains fit for human consumption are all considered safe.