Chief Keef -- LOADED at LAX

Chief Keef can make it rain anytime anywhere ... just ask the giant wad of bills he pulled out of his pocket ... like it was nothin' but chump change.

17-year-old Keef was waiting for his ride outside LAX Saturday ... when our photog struck up a convo about weed (what else?) ... and right in the middle of it Keef interrupts him to flash some cash.

We're talkin' STACKS of bills (100's & 20's) -- several inches thick -- probably adding up to thousands of dollars. It's not the first time he's done it either ... McD's and the cops have all been privy to Keef's cash rolls.