Library visits, board books, magnadoodle, building with duplos, dry erase markers on the windows, anything with water, sorting colors of tiles in buckets.
FWIW, neither intellectual stimulation nor physical activity prevented tantrums here. The only thing that helped was time.
The best thing I did for my littles was to scoop up 2/3 of their toys and put them in the closet in two "sets". Every so often I exchanged the toys that were out with a set of toys in the closet. They were always very happy to play on the days I changed out the toys.
