Everybody's got 'em. A favorite, cute, most comfortable pair of something that they just love to wear.
Since Leah is too young still to get a vote, I'll throw in my two cents for her:
Striped pink and white with a fuzzy little lamb near the top, she's been wearing these jammies since the first day she fit into them. Although "fit" is overstating things a bit, since she used to just swim in them. They're 0-3 month, but somehow she miraculously still fits into them - now her legs and arms actually come out where they are supposed to!