What's a cold, portable adult beverage I can bring to a "Margaritas on the Beach" party, other than a Margarita?

Tonight, the complex that i live in, which is on a lake, is having a “Margaritas on the Beach” party. They are providing food and mix for Margaritas. It’s BYOB, you can bring tequilla or whatever you want to drink. I am not a big drinker, so i don’t want to buy a bottle of tequilla and make two drinks or three drinks from it, and have it then collect dust in my kitchen for years to come.

What is something I can bring, maybe a pre-bottled drink, that is alcoholic but is something other than tequilla. Wine coolers? Something else?

Please suggest something that would go with a night time summer party on the beach.