Izabel Goulart Rocks Skimpy Bikini on Beach Outing with Fiancé Kevin Trapp

Izabel Goulart seems more into white sandy beaches than a traditional white Christmas ... living it up in the Caribbean with her fiancé.

The model and former Victoria's Secret Angel soaked up the sun and surf in St. Bart's Saturday ... flaunting her curves and toned tummy in a tiny white bikini.

Goulart grabbed a paddle and played some games with friends on the beach ... running across the sands and smacking the yellow ball back and forth with the crew.

At one point, Izabel had to chase a ball down and bent over to pick it up ... leaving little to the imagination when it came to her pert backside.

Goulart's future husband, Paris FC Goalkeeper Kevin Trapp, looked ripped in just a pair of swim trunks ... proving the world's most popular sport certainly keeps ya fit.

BTW ... Goulart and Trapp aren't the only big-name stars on the island this time of year. Heidi Klum and her husband, Tom Kaulitz, are also enjoying some fun in the sun on the island -- with Klum even ditching her top for a little skinny dipping.