Abstract toys are a good idea, we've got a few sets of those for kids to play with. I remember the tub of Legos I had growing up and how much fun that was building things with it.

In addition to abstract toys, I'm looking for things that parents wouldn't normally have access to. Many kids already have Lego sets but they probably don't have something like this http://www.amazon.com/gp/product/B00008BFZH

Chemistry sets wouldn't work well for this program because they're single use but electronic sets could work well. I ordered this game for the program http://www.amazon.com/gp/product/B00008BFZH/ref=oh_details_o01_s00_i00?ie=UTF8&psc=1