Egg cartons - and you can get little plastic eggs around Easter time to use as counters in them, in the meantime using whatever you have around or can find cheaply. You can also make pom pom balls of yard to use in them. You can even get very big cartons (25 holes or so) at restaurants that specialize in breakfasts - so they can make a 100 hole piece.
Coins, paper money (maybe play money would be a good idea), a toy cash register, acorns or eucalyptus pods, ice cream sticks with beans glued on them for counters, Hershey bars (see Hershey Bar Fractions
), raisins, measuring cups, crayons for drawing math pictures, heavy paper for making charts, sandbox to play in with all sorts of things, hopscotch, large unchokable sized beads (you can even make some special ones of your own with plasticene clay!), skipping, singing, rulers and yardsticks, string or ribbons, measuring tape, quilting pieces to go into your own quilt, clay...
Take a look at this article for lots of fun ideas:
The Delights of Exploring Math with Your Child