Check out these suggestions.
Celery sticks with peanut butter and several raisins on top
Rice cakes with peanut butter (good for getting a protein punch)
Low-fat cheese cubes
Hardboiled eggs
Deviled egg (wrapped in plastic wrap)
Fruit yogurt cup (add in some fresh fruits or nuts for a boost
Trail mix
Nuts or nut mix (stick to just a handful)
Vegetable sticks with a little packet of dip (lowfat salad dressing packets found in salad bars work as easy-to-pack dip)
Broccoli or cauliflower bites
Half of a turkey or tuna sandwich on whole-wheat bread
Cucumber slices (lightly salted or with nonfat Italian dressing)
Yogurt and granola
Leftover chicken or turkey slices (great to eat cold)
Healthy fiber-rich or grain cereal (great to eat dry from a baggie)
Pickles (wrapped in foil or plastic wrap)
Box of raisins or other dried fruit
Half a large whole wheat bagel with light cream cheese
Apples, bananas, strawberries (any fruit works, these are naturally portable)
Mixed berries (these freeze well in plastic bags)
Whole-wheat crackers and low-fat string cheese
Grapes in a baggie
Fruit smoothie in a thermos
Tuna and cottage cheese in mini-containers