baby carrot packs are awesome for that sort of snacking
so are kid's fruit snacks ( and you can pick neat things like my little ponies or nemo or trains or disney princesses

)
popcorn is great for when you are near a microwave, but that's probably not often.
pretzels are great for -on the go- times
peanut butter crackers or prepackaged nuts are a good source of protein when you're on the go, but they aren't very filling.
slimfast and special k both do on the go meal bars, too. they both have the problem of leaving you hungry, too. Clif bars are probably the best energy bars out there. they are -very- good for you, and taste great. they have so many flavors it's amazing. verry balanced and quite filling.
it's best when dieting ( and being a vegetarian) to think of food in terms of side dishes, i think.