Make your own bowl covers

Make your own bowl covers from old vinyl table cloths or shower curtains. To be extremely frugal, use elastic cut from old clothes. Cut a circle, using a dinner plate for a pattern, and cut a piece of elastic an inch or two shorter than the circumference of the bowls you'll be using (a little more or less won't matter much). Sew the elastic around the edge of the plastic circle, gathering as you go. Make larger and smaller covers while you're at it.

Cap your bowls

A shower cap makes a great bowl cover when you want to store something in the refrigerator. It's cheaper than plastic wrap because you can use and reuse and reuse it. Wash it with your dishes (not in a dishwasher) or, if it hasn't touched the food, rinse and air dry between uses.