Think of little things you have around such as:
dry macaroni noodles
small rubber balls
game pieces such as checkers
Mix the items all together in a bowl or pan and then show your child how to sort the like things together in each muffin cup. After they do it a time or two, you could make it more challenging by having them sort by color, size, or shape instead.
To make it more toddler-friendly, choose just a couple of categories and maybe three of each item. They may need lots of guidance and praise to get the hang of it.
Of course, if your child tends to puts things in their mouth, DO NOT use any items that would be a choking hazard. Stay close by while they sort, just in case! This may be a good activity to do while baby is napping.
And I would advise not using food items like cereal pieces that will get mixed with dirty coins. I'm sure they can find their immunity-boosting edibles somewhere else.
Let's teach those organizational skills early on! Just think of the pay-off when they reach adolescence. Surely this will translate into neatly organized closets and dresser drawers...surely.