Harry Styles Rande Gerber's Fueling My Birthday Party With Tequila!!!

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Harry Styles walked away from his lunch with Rande Gerber with the greatest doggy bag in history ... 20 cases of really good tequila!

Turns out it was an awesome pre-birthday gift for Harry, who turns 22 February 1st. The tequila is Casamigos -- the brand Rande owns with best bud George Clooney.

We're told Harry will make good use of the booze ... he's throwing himself a birthday shindig this weekend at an L.A. estate. 

Why the gesture, you ask? Rande and Harry have been friends for a while ... and tequila is what you get from Rande, which is way better than having a best friend who's a stamp collector.