I love activities that are cheap, easy, and entertaining for more than just a minute. This is one of my favorite “go to” activities to do with bored kids. All you need is a handful of completely random objects and/or toys from around the house and a bag.
Before you show them anything, have them stick their hand in the bag and try to guess what is there.
Have them sort the objects into categories that they come up with (color, material, use, shape, etc.)