I saw this in a MothersClick newsletter and loved the idea:
Fill a large plastic container with uncooked rice. Under the bed storage containers work well (I have one similar to this – it’s small enough to carry so I can store it in the garage and bring it out for play). You can buy huge bags of rice at warehouse stores like Costco.
Give your child anything she might use to play with sand. Shovels and cups are a good place to start. Bury toys for her to find. And take the opportunity to teach her new words by identifying the objects she’s playing with.
To make clean up easier, place the container in the middle of a large blanket. Keep a handheld vacuum nearby too.
A final tip from the article: Tell your child before she starts playing that the rice must stay in the box and utilize the “three-strike” rule.