Conor McGregor -- SPOILS OF VICTORY ... Rolls-Royce and Mariah

Conor McGregor is starting to upgrade ... rollin' around Santa Monica in a $500,000 CAR!!!!

Check out out the footage of the Notorious One ... doing some Christmas shopping in his Rolls-Royce Phantom Drophead Coupe ... while bumping old school Mariah Carey.

Don't judge him. Old school Mariah is dope.

As for the whip, it's just a drop in the bucket if you consider the fact UFC boss Lorenzo Fertitta just came out and said he expects Conor to be the UFC's first $100 MILLION fighter.