GTA V: Infinite Money
I was tipped off to some money and guns on this blog I follow and figured I'd make a video to confirm. I didn't find the guns...don't have the lung capacity yet to search around...but I will later. At any rate, they should be around that same general vicinity.
Oh and the other item I swam towards (but didn't pick up) was a healthkit. Just in case you lost some health drowning, ya know. Or got bitten by a shark ;)