I did this back in the day too! At the beginning of every school year we were told we needed to have all our books covered. I used brown paper bags mostly, but sometimes we were given covers with the school logo on it and some ads for local companies. The book covers usually lasted a couple weeks, then they got torn off and I don't think anyone ever recovered them. You didn't see a lot of covered books past the first month of school.
Stores around here give you plastic bags unless you request paper.