What should I cover bread dough with while it's rising?
The goal is to keep the surface of the bread from drying out.

A wet towel works fine but plastic wrap is cheaper and easier than constantly cleaning wet towels.

I have used both methods and haven't noticed a difference in the bread produced. In very dry climates, when I made bread with multiple rises I sometimes had to redampen the towel which was an added inconvenience.

Lately I have been proofing large batches of bread in a large stock pot and just use the lid of the pot as the only cover.