George Clooney's BFF Rande Gerber -- Tequila for the Groom ... I Got 50 Cases!

George Clooney is getting a big discount on booze for his wedding, with the help of best friend Rande Gerber ... who's flying more than 50 cases of tequila to Italy for the big shindig a week from Saturday.

TMZ got video Monday of Randy leaving L.A. for Italy in a private jet ... loaded with at least 50 cases of Casamigos tequila ... the company owned by George and Rande.

The video is fantastic ... Rande drives up in a blacked-out black Mercedes right to his jet, where he inspects the precious cargo ... then has one of the guys cut open 2 boxes. Cindy Crawford's hubby then removes one bottle of Reposado and one bottle of Blanco ... then proudly fist pumps them as he boards the jet.

There are numerous reports in Italy ... the wedding is set for a week from Monday at Cipriani hotel in Venice.

Arrivederci ... and recuerdos a todos.