As long as your preschooler is supervised properly or beyond the age of mouthing items, sorting Grandmother's button jar contents into an egg carton BY TWEEZER is a great math activity. This kept the Princess busy for quite some time. Older brother tried it for a mere minute or so, declared, "This is just annoying!" and went off to work a brain bender puzzle.
Window clings are great cheap manipulatives. My daughter likes to play with them on the glass coffee table as kind of a matching activity. This one was money.