Here are two quick sets of manipulatives to help with the teaching of fluid capacity. The primary, simpler one has only gallons, quarts, pints, and cups. They are in logical shapes and sizes to show the interrelations in the parts of a gallon, like a cup is 1/16th of a gallon. A quick conversion chart is supplied.
The secondary set is more complicated, showing how a gallon is 128 oz, so there are 128 boxes. This set includes the quarts, pints, cups, and ounces, along with a few more conversions.
Cut them out and go to town! Makes a great center and it's way cheaper than buying something plastic that kids can't keep!