I store my paint filled egg carton sections in a shallow tub with a lid until the section uses the paint. The egg cartons get a little soggy after a while, but works great for about a week period of time. Saves on paint waste! - now I've used the egg carton thing with the egg carton lid to use the paint over a few days but why did I never think of putting them into tubs with lids!! this is why I love pinterest!
Also on these boards
Egg carton art! Love this!