Various food and drinks are mentioned throughout the Potterverse, so making those recipes for your guests is a great party idea! We have collected traditional British recipes as well as Potter-specific recipes here for you to use, ranging from very simple, purchased ideas to elaborate edibles!
For those looking for their own inspiration, the HP Lexicon is an excellent source for the food and drink mentioned in the Harry Potter novels.
Although specific recipes like Pumpkin Pasties and Treacle Tarts are tasty and a lot of fun, you do not have to run yourself ragged making all your party food from scratch. Think of normal party foods & come up with Potter-related names for them.
So many things can be "wands" - pretzel rods, breadsticks, licorice sticks...
Ready-to-heat frozen party taquitos or ready-made sliced torilla wrap appetizers can be "parchment scrolls" or "homework scrolls"
Ready-to-heat frozen chicken wings can be "bat wings"
Bertie Botts beans are great but very expensive, so buy a few boxes or bags and mix them in with normal Jelly Belly beans. Your partygoers will still stumble upon the occasional "vomit" or "earwax" or "sardine" but you won't be broke just from buying your party candy. :) (Unfortunately mixing Bertie Botts in with the larger, cheaper jelly beans makes it a bit too obvious which ones could be the yucky ones!)