Guessing Game

I'm trying to resist the urge to post a picture of every Etsy treasury that features a Yellow House Knits sweater (gorgeous though they all are!).  But this one posted by La Bella Joya was just too clever to pass up. 

This collection of a collection of seemingly unrelated items does have a theme.  Can you guess what it is?  I had to think about it for a while, but I finally got it--only to discover that someone else already had the same idea.  If you think you know (or you're stumped), click on the treasury to see what we guessed.