I would suggest a complex carb and a protein, with or without a tiny bit of unsaturated fat. Like a half sandwich on one slice of lightwhole wheat bread with lean turkey breast and mustard with a little tomato and lettuce, for example. The bread is 40 calories, and 2 oz. of turkey would be about 50 calories, so for about 100 calories you'd have a really filling, healthy snack that would tide you over for a while. Eat it with a 20 oz. glass of water and 1/2 a cup of frozen (defrosted) mixed berries (35 calories) and you're good to gofor a WHILE!
No offense, but I'd avoid jerky (sorry!)
-- lots of sodium, nitrates, and preservatives. The portability factor is nice, but you could choose something much healthier and with more lasting power.