I just discovered this kit at Rockler to quickly turn any piece of plywood into a rolling platform with brakes. It's curently on sale for $40 and if you sign up for their email you get free shipping. I have no idea what I'm going to use it for, but that's going to come in very handy someday.
https://www.rockler.com/port-a-mate-pm-1100-plywood-mobile-base-kit?sid=AFU9#
https://www.rockler.com/port-a-mate-pm-1100-plywood-mobile-base-kit?sid=AFU9#
