This is the kind of stuff that I take with me when I've got to eat on the go. On my current schedule, that's pretty much every weekday:
-- Granola Bars -- I like Fiber One bars: high fiber, mostly clean carbs, decent amount of protien, relatively low fat, sugar & sodium compared to most alternatives. Some flavors have better macros than others, so read the labels.
-- Power Bar Harvest -- As above, better macros & lower in processed sugar than most alternatives. Ditto on the labels / flavors.
-- Apples & banannas -- Easy to eat in a hurry without making a mess.
-- Whey powder -- Bonus points if it's pre-portioned into a shaker bottle or sandwich bag before you leave the house.
-- Fat free yogurt -- It doesn't keep very long without refrigeration, but a single serving container of yogurt is very portable.
-- Raw almonds, cashews, etc. -- Healthy fats. I have a tendancy to overeat these if I just snack on them, so I never take more than a single serving (1 oz) with me.
-- Tuna fish -- The single serving foil packets are easy to eat right out of the bag... as long as you don't mind the taste of plain tuna.
-- Instant oatmeal -- Not as good as the real thing, but still an option if you have a microwave available.
-- Disposable plastic "silverware" -- If you pack yogurt, bring a spoon, if you pack tuna, bring a fork, etc. This is the thing I most often forget to pack.
Anyway, that should give you a few ideas. You could also get one of those thermal lunchboxes and an ice pack, which would give you even more options (pre-made wraps, pre-cooked chicken breast, fresh veggies, etc.).
Also, Zip-Lock bags are your friend.
-DR
Edit: mex0050 beat me to some of this stuff. Also, mex - love the sig. RIP Mitch.