We had a princess party when K turned 4. It was nice weather so we had it a local park in a pavillion. Everyone brought their dress up clothes (I took every dress up outfit, frilly night gowns, halloween costume, shoes, stuff from my house too) and we cut out fabric to pin on the boys shoulders for capes and bought the foam crown sets from Hobby Lobby. Everyone brought craft leftovers, glitter glue, peel and stick foam shapes, gem stones, feathers, etc...and the kids used the foam crown shapes and made awesome head ornaments. We used a backdrop on the wall and each person had an individual picture taken in full dress up.
Since this was going to be a lot of lot of fun I didn't want to take time away and make the cake so we bought one from Wall-Mart or Albertson's, it was tall and shaped like a castle. Be aware the cake is small, the pic looks large but it was very small.
She lot several princess themed toys like Barbie, coloring sets, books, and then lots of dress up jewelry, tons of hair stuff like hair bands with lots of fluff, headbands with lots of shiney bits on them, etc...anything that looks like bling.
We let her keep some of the hair stuff in her vanity so she could play dress up with it/start learning to manage her own hair/whatever she wanted to do. And yes, I had to pick all of it up off the floor most evenings. She highly enjoyed these toys and still plays dress up with her hair stuff but at 5 is much better about picking them up herself.