The nightlife magnate, who co-owns Casamigos Tequila with the George, was spotted loading up his private jet with more than 50 cases of the tipple.
Rande, who is married to supermodel Cindy Crawford, was seen arriving at the landing strip in a blacked-out car and inspecting the boxes.
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Rande Gerber and George Clooney (pictured on a previous occasion) aboard their private jet
Cindy's husband then pulled out two bottles and fist-pumped the air, before boarding the plane headed for the wedding destination.
The two friends set up the tequila brand with another close pal Mike Meldman, after deciding to share their favourite tipple which "they serve at their homes in Mexico" with fellow aficionados. Several years ago, George and Rande built holiday homes in compounds next to each other in the Latin country.
Recent reports suggested that the Oscar-winner has asked Rande to be his best man – contrary to previous speculation that Brad Pitt would be playing the role.
Rande Gerber and George Clooney co-founded their tequila brand
George's bride-to-be Amal Alamuddin is said to have asked her younger sister Tala to act as maid of honour. In keeping with tradition, the lawyer's parents are also believed to be footing the wedding bill while George is expected to cover some portion.
It is thought that the Hollywood hotshot and his belle will marry in Venice, Italy – where they first met.
The couple, who posted their wedding banns in London's Chelsea Town Hall last month, will reportedly host a three-day celebration. The big finale is believed to take place in Ca' Farsetti, a palace in Venice facing the Grand Canal.
Amal Alamuddin and George Clooney will marry in Italy, where they met
"I met my lovely bride-to-be here in Italy, whom I will be marrying in a couple of weeks, in Venice, of all places," said George earlier this month, as he accepted an award for his humanitarian efforts in Florence.