Make a Portable MiniSandbox » Dollar Store Crafts
You can get rocks, shells, and other trinkets to add to the sandbox, if desired. The dollar store also has an array of beach sand toys at this time of year you can get. I say just use what you have on hand, though! The sand: you will most likely need to hit the local home improvement store for some sandbox sand. I bought a 50 pound bag of it ...