My daughter had a sleepover for her 7th birthday. I let them each frost/decorate 6 cupcakes each with different colors of icing, sprinkles, etc., we did a craft I had bought at Michael's, had pizza for supper, watched a movie and then lights out.
At seven you can do a small craft, watch a movie, have music and a ton of balloons for dancing and otherwise being obnoxious :0), you could get a few party games- pinterest if FULL of ideas, Do cake and presents first... then there is a ton of new stuff to do that you didn't have to buy. ;0)
Craft ideas: friendship bracelets, beads---Hearts, and letters are huge at this age, tissue paper flowers or melty beads even but I know right now bracelets are The IT Thing right now with DD and her friends who are all turning 7 around this time.