Best thing I've bought (at least that I can currently remember) is a set of swim trunks and a tee. I'm a big guy so I was amazed they had my size. Also, since I was soaked from Splash Mountain, and it was freezing cold at night, it was really practical.
Worst thing: Lollipops! Those things are so freaking cute, and everyone at home asks for them whenever I travel to California for business, but no one eats them.