Hellobee Boards

You could make bags for them to put in a small rubbermaid box if they have one or get them a little tub with different sensory materials in bags. E.g. Kidney beans, with cars, trucks, little sticks (constructiony type things). You can mix up a batch of "moondough" 8 cups flour: 1 cup baby oil with some little shovels or spoons.-It smells amazing and you can scuplt it, sort of like kinetic sand, but different. A bag of dirt with fake bugs and little fake plants. Water beads are also really really cool: http://waterbeads.net/buy-water-beads/. You can often find packs of multicoloured ones and they only take a day or two to soak up water and then you can put toys in with them, squeeze them, and bounce them in a little container. Hair gel mixed with food colouring (dollar store) in a ziploc bag. You can also provide a box or two of cornstarch and some food colouring bottles with a recipe for making "goop": http://www.instructables.com/id/How-to-Make-Goop/ If you go the bags route you can give them different stuff they'll be able to play with at different times. On the plus side, all the stuff to mix up some different sensory bags and even buying a bin for the child probably won't be that pricey!

I just bought squigz for my nieces 4Th bday. The popping sound they make when you pull them apart is oddly satisfying and they feel nice in your hands.

http://www.amazon.com/Squigz-Starter-24-piece-set/dp/B00DEBB3N0