Who doesn't love a super cold, extra foamy coke float? Here's an idea to spruce up your regular ol' "Coke Float Party"... throw in a flick! Not the kind of flick your older brother would give you when your mom wasn't looking... the movie kind that everyone enjoys!
Another way to "float" this event is in the pool. Show a flick at the pool and provide pool noodles/floats so people can float with their floats (drinks) and enjoy the flick! Of course you can also offer other sodas to 'float' other than coke... root beer, sprite, etc. You can serve/make other things other than floats, as well: fudge, cookies, cupcakes, etc.
Have a local brewery near by? In addition to beer, most breweries make their own root-beer. It's a great way to get a vendor involved. Call them up and invite them to come hand out samples or pay them to come cater their root-beer (and other beers) for your event.
Food...must have food! The obvious choice would be popcorn to go along with the flick. Spice this up by offering lots of different flavors (cheese, caramel, candy, kettle). Picture the giant tins that come out around Christmas time, or check out our gourmet Popcorn Bar board on Pinterest. Have a local candy shop or a specialty popcorn shop around? Invite them to come out to cater or hand out samples. This is another great way to include a vendor and support a local business!