Are you serious?
This guy actually threw a bottle at you?
Even without the radio, get his numbers and boat name and report him when you get back.
There is no rule in open water about slowing for other craft, but common curtiosy does apply. SOME PEOPLE ARE FRIGGIN MORONS.
Last season, while putting along in the "no wake" zone, a 30+ footer ahead of my 21 and to my starboard side made an abrupt hard turn port, cut me off so bad I had to hit rev to stop my forward motion, or CRASH. Then did the same to the kayak on the other side of me. he never even looked b4 turning. I was fuming made as was the yaker'. I was going to follow him to his marina and chew him out in front of his "dock mates", to embarrass him, but I let it go, I figured it just was not worth the aggravation. .
Oh Sorry as for you question.
any hand held would be fine, one with Ni-Cd batteries is better, but the batts don't last too long, a couple of seasons (unless you take real good care of them). Get one of those water-proof floating bags for it too. A guy a work here is a yaker' I'll ask him too.