Crackers work well. Snackwells are a little lower in fat. They have crackers, cookies, and other snacks.

The Nutrigrain bars that are filled with fruit are okay. They fill you up and have a bit more pleasant flavor than the power-type bars.

You could also consider whole pieces of fruit. Oranges and apples would keep for a week and wouldn't get bruised if packed well. Even carrots, washed ahead of time and packed in something breathable would probably last the first 2-3 days.

They also have lowfat peanut butter, so don't rule it out altogether.

Pretzels are low in fat and yummy. Get the small stick shaped ones, as they would probably be more efficient in the amount of volume they would take up.

They also make shelf-stable jello and pudding. Pudding would probably have more fat than you're looking for. There might be some lowfat kinds though.