A paint-chip synonym garden! The colors on the paint strip are similar, but not exactly the same, just like the synonyms themselves. Think I'll try this next year and add an antonym to the last space, as suggested by the original poster.
I could totally do this with money-- dollars on a pumpkin then popsicle sticks with bills and coins that add up to the amount. Addition/subtraction sorting - child needs to determine which sticks add up to the number on the bucket.