I agree with everyone else, dont take much cause they make their own fun.
But, that said, there are some trusty family faves I always take like a footy and the cricket bat, bikes (my son had a trailer bike for a while), matchbox cars for the dirt, buckets and spades for sand or the creek, a kite (I have a pocket one in the glove box) and something for the car - DVD, DSi or iPOD.
Hope this helps,
J