The Beatles Are a Natural Party Choice
A party theme should be something easily recognized by the guests. It should also be something the guests can get into easily, and inexpensively, such as by wearing a part of a costume that will be readily recognized. Parties often have food and drink, so finding something to serve on would also be a plus, but if you cannot find Beatles party supplies generic solid color plates, cups, and napkins will work well. But, and this is the real important part of a theme party, decorate with the theme in mind.
One way to get your guests right into the mood is to offer a pair of brightly colored John Lennon glasses as you greet them at the door.