I noticed you're in Canada, and I'm not sure if they have these there, but Carnation Instant Breakfast drinks are wonderful. The chocolate ones taste like plain chocolate milk, and while they do have a significant amount of sugar, there is also a lot of protein. They're also really nice because you can just kind of sip them as you go along. I really like peanut butter balls at my meets, but you may want to take "All Chalked Up's" comment into consideration. The recipe below is what I use they're actually pretty healthy. They pack well and are conveniently bite-sized. Some other things that I bring are squeezable fruit pouches, string-cheese, Emerald Nut breakfast pouches, oatmeal-to-go, granola bars and fresh fruit. Plain air-popped popcorn is also really good. It's even better if you add a little brown sugar and cinnamon, but again that's added sugar.
Peanut Butter Ball Recipe
1/2 cup Oats
1/4 cup Honey
1/2 cup Peanut Butter
1 cup Powdered Milk
1/8 cup Ground Flax
Rice Krispie Cereal (Optional)
Mix together and but into balls. Roll in Rice Krispies for an extra crunch. (Optional) This recipe makes enough, but not a ton, you can double or half it for more or less.