My DD’s all-time favorite toy right now is a recycled parmesan cheese shaker. She uses one in the bathtub, one at my parent’s pool, one with the bean tub, etc.
I am into recycling and reusing to a point of it being a bit OCD LOL! If it scoops or sprinkles, I most often save it (spice containers, laundry detergent scoops).
I also have some plastic tongs in DD’s bean/pasta tub. I LOVE the idea of hiding bugs and/or plastic flowers in it. I need to make a run to the dollar tree.
I also have a sand tub (another plastic tub with a lid). All three of our littles like this. Actually I use it with 12YO and 9YO for a different way to practice spelling words.
We use it only outdoors, but that is another idea if you school outside some. Can use the same manipulatives you would have in your bean/pasta tubs.
I have hidden coins in it for DS and DD to find, and then we work on naming the coins as they find them. You could use that idea with many things.
Please keep the ideas coming.