Yummy Yucky by Leslie Patricelli
This is currently Second Son's favorite book. (He's two and a half.) We've read it so often to him, he knows all the words.
Ms. Patricelli contrasts yummy things (like "Mommy's cookies") with yucky things (like "Mommy's coffee," though we always say "Daddy's coffee" because Kansas Mom only drinks tea). Second Son just laughs and laughs, especially at the end when a whole page of "more yucky things" includes stinky socks. For some reason he thinks the stinky socks are the best part of the book.
My other favorite Leslie Patricelli book is The Birthday Box in which a box is indeed the best birthday present.