All you need are some glass jars and matching lids, a basket to contain them all and a carpeted room for your children to explore the jars in a safe environment. I was really nervous letting my kids play with the jars, but then I realized that part of the Montessori philosophy is about teaching children to handle real-life objects and to learn to respect and and be gentle with the materials. So the activity isn't just about screwing lids on the correct jars, it's about learning to properly handle different materials, about determining size and shape, about manual dexterity, about volume and weight, and a plethora of other mathematical concepts. Did my kids realize this when they were playing with the jars and lids? Well, no, not consciously. But I believe they were learning these things in subtle little ways that they probably didn't realize.
Anyway, enough on that. I had the kids start by just handling the materials--screwing the lids on and taking them off. Then we experimented with sorting. We sorted puff balls by color and then by size. I occurred to me that it would be interesting to sort beans or other hard objects because then you have the added benefit of the sound the objects make when you fill the jars. Both the kids realized that the jars had a scent to them (because the jars were washed out spaghetti sauce and applesauce jars, and had maintained some of their scent) and began smelling the lids and the jars and matching the scents--this was sort of silly, but I thought it was interesting that it occurred to them to sort in this manner. Little Bean was really attracted to this activity, which surprised me; I had intended it for Miss O since it seemed simple and easy for her to accomplish. This will definitely be one that I bring out again and again. Try this and see what your little ones think!