Or make a Bug Village. Directions here.
Paint numbers on them, put in a cup, give a shake, and pour 'em out to create a game. What are the rules? Not to worry, you'll make 'em up as you go.
If you've got ends of candles, melt the wax and fill up the acorn caps - add a short wick to each - and you've got tiny candle boats.
And if things are too quiet, try making an acorn cap into a whistle. Directions here.(full disclosure: I have yet to get my acorn caps to whistle)