Model Ava Sambora Shows Off Her Buns

Ava Sambora's just starting out in the biz, but she's got this model thing down pat -- slip into a tiny bikini, hit every celeb's fave island hot spot ... then rinse and repeat.

The 18-year-old splashed her bikini bod in St. Barts over the weekend, and topped off her tropical look with what looks like a piña colada.