Frugal GM Quick Craft Tip: Flexible Cutting Boards
Normally sized 12" x 15" or larger, these things usually run about a buck or two a piece and often come in packs of three or four.
I like to use these for the obvious purpose of protecting my work surface from getting cut up, but they also work great as small mobile work surfaces. You can paint terrain pieces on a board and then pick up and move the piece using the board. I've also used them to dry tea leaves for flocking, and they work great as stiff, yet flexible templates. Cut them using a leather scissors or hot knife. Definitely cheaper and sturdier than using many template acetate sheets out there.