One of the things my son loved was moon sand. We got a lot of moonsand for him and put it in a big tub and allowed my son to play in it. He was able to squish, push, and of course build and sculpt this stuff to his hearts delight.
Pros: This is a great activity for tactile and proprioceptive senses as well as give mommy a break. It also doesn't get stuck in carpet or on clothing.
Cons: It can be very messy and expensive
Solutions: A wonderful solution for this is going to the dollar store and picking up a $1 shower curtain. Place it underneath the tub or whatever you have the moonsand in. When the kids are done playing with their moonsand you can pick up the edges and pour any moonsand that fell out back into your tub. It's really easy if you have them working on it on the floor because you don't have to move any tables or chairs. :) Also, in another post I will be posting a recipe to make your own moonsand at home that I found on the net but it is a HUGE batch. I have not tried this myself at home but it looks like it would be cheaper than buying it from the store.