What you need:

Rice or dry pasta

Different sized plastic cups

Large bowl/deep filling tray

What to do:
On an easy-to-clean floor (such as the kitchen) why not fill a bowl with rice or dry pasta? (Rice is nice and pasta is faster? Or is it?) It will keep your toddler entertained while you can get on with your own thing nearby (just keep an eye on their safety and ask a few questions now and then). Your little scientist will love learning how different materials behave by filling up the cups and pouring them back out into the bowl. Just burying their hands in the bowl will feel nice and help develop their coordination.