I read a ton of Montessori learning blogs and have read a lot on sensory tubs. Sensory tubs aren't necessarily a Montessori activity but they seem to go hand in hand with each other. I've wanted to make Bean one for awhile and thought since her birthday is coming up, I would try a birthday-themed tub. If you aren't familiar with sensory tubs, Counting Coconuts has a great post all about them.
I found a recipe by Two Little Seeds for Rainbow Rice. I used neon food coloring and the colors turned out really bright and festive.
I used balloons, candles, small erasers shaped like cake and ice cream, some Mickey Mouse favors since she will be having a Minnie Mouse themed party, some small butterfly favors, craft sticks and some bouncy balls. I gave her a colorful ice cream spoon to use to dig through the rice. I found all of these items as well as the green tub to hold it all at Dollar Tree. It all cost about $25-30 dollars but these are items that can be used with other themes later on, so the cost wasn't that bad.
Bean loves this activity. She isn't allowed to take any of the items away from the tub which makes them a little more special since she can only play with them while working on the tub. She also has done surprisingly well with keeping the rice in the tub. She "lubs actibities". She asks to do it daily and she usually spends a half hour on it at a time.