There are actually quite a few good, cheap, healthy things you can do. Fruit, like grapes, apples, etc make excellent snacks - and the fiber in them makes the natural sugar release slower (decreasing the chances of hypoglycemia).

Peanut butter crackers (just a little peanut butter per 2 crackers), or if you think you'll be hitting a real low, peanut butter on graham crackers. Along the same line, slices of cheese on crackers (you can make them ahead of time and put them in a Tupperware like container). String cheese in the package from the cheese aisle makes a good snack with a protein punch.

And then there's always rice cakes with peanut butter... or peanut butter on celery. Actually peanut butter on anything portable!