Frank (on the long side of 2 1/2 now) has two favorite distinctions with which he likes to identify... as much as possible.
distinction #1 - yummy or yucky
He is delighted with long word or picture card games in which he gets to identify things as yummy or yucky - even if they don't fall remotely into the category of food. In fact, I think the distinction is simply edible or non-edible in his head (not a real picky eater just yet).
distinction #2 - good guy or bad guy
Almost every time we watch a movie or he finds pictures in a book he enjoys labeling everybody as a good guy or a bad guy.