I've picked a few berries in the Sierra here and there, and wild onions, and even picked up a trout once that had beached himself and was flopping around (and caught a few on a hook, of course) but mostly where I hike edible stuff is not so profuse that I could significantly forage without damaging the ecosystem.

Locally in the SF Bay Area I took a class on wild edibles and we sampled lots of stuff like pancakes made with curly dock seed (a weed related to buckwheat - we called it "Indian tobacco" when I was little - made very delicious pancakes 50/50 with Bisquick) and elderflower fritters; tasty and interesting, but mostly requiring other ingredients to prepare in a tasty fashion, so not so practical for backpacking.

However, when in Maui once we took a hike with a guy who had lived off the land there for a few years back in the 60's. He had amazing knowledge of all the edibles, and had us sample stuff as he led the hike. Lush tropical areas would not be so prone to over-foraging, and I wouldn't have a problem with the ethics of eating off the land when it was so heavily productive. As long as there weren't scores of others like me doing the same thing, anyway.