A couple noone has mentioned yet are snow peas, salad leaves and sprouts.
Snow peas are excellent. They last for ages and don't mind getting bumped around.
Mixed lettuce and salad leaves sold in those sealed bags are also good if kept in the top on the pack where they won't crush, but not in the summer time. Other seasons, they are just fine and again last for a long time, especially if you can get them with a long "best before" date to start with.
Sprouts that you grow yourself are great for really long bushwalks. If they are just sprouted when you leave, you only have to rinse water through them a couple of times a day and tuck them in an outside pocket upside down so they drain as you walk. I use an old plastic container with a screw lid that I drilled holes into. By the time all your other fresh fruit and veggies are gone, the sprouts are ready to eat.