I just found over the weekend that you can stay underwater in a car forever without running out of air. I had a bounty and equipped my re-breather, hopped in a random car & drove it off the pier. I figured I would just ride it down to the bottom, and when it landed & stopped sinking my air meter disappeared. It would return if I moved the wheels, but if you just sit there you can stay as long as you want, just don't get out or you can't get back in. I sat out a bounty in the car and a few people swam down & tried to get me. They don't seem to be able to pull you out of the car & stabbing the car didn't affect me inside. Probably well known but it was new to me.
Also, do the baseball bat & crowbar spawn anywhere on the map online? Mine disappeared at some point & I want to get them back. I already got the golf club back, but haven't found the others outside of doing one of the deathmatches or LTS's that have them.