I bought a couple of big bags of rice at Aldi ( I may add one more next time I go) and poured them into this "under bed" storage bin. It is low to the ground so that Pickle can easily access it and it also fits under the train table when not in use. Add some trucks and you have an instant preschooler construction zone.
A few pieces of rice do make it out of this from time to time, but our rule is that if he makes a mess, he has to pick it up before moving onto another activity. So far he has done a great job with it.
There are endless variations to this idea ( more to come on this in the future) but one of our other favorites is to clean out the rice and put in some water and some cups to practice pouring with. You should never leave a child unattended with water so make sure you are able to give this activity your full attention before beginning. On warmer days it's fun to put in an ice cube and observe as it melts. Also, try freezing some ice cubes with food coloring in them and watch and see with your child what happens as they melt and the colors combine.