Drew Brees & Matt McConaughey -- TOSSIN' BEADS ... In French Quarter

Here's a cool video ... New Orleans Saints QB Drew Brees hangin' out on his balcony with Matt McConaughey ... and tossin' out beads to people on the streets.

So ... why?

The guys teamed up to hand out clues and rewards in a scavenger hunt for charity -- and one of the challenges was to go to Drew's pad and sing to the guys ... in exchange, participants got beads.

It was all to benefit Matt's "j.k. livin" foundation and Drew's "Brees Dream" org. -- but you can tell the guys are having a blast together ... and even got their families involved.