For ease of transport, taking beer from the kegorator in the boat, to parties, etc I use these hommade carbonation caps:
The Schrader valves are ~$1.25 each and a cap takes 10 seconds drill a hole in and set up. It works pretty slick - picnic tap the beer right into the bottle at a low PSI, squeeze the small amount of foam out until there is zero headspace, and tighten down the cap. Then blow 15 pounds CO2 into the bottle with a tire chuck that's hooked up to the CO2. Shake slightly to replace some of the lost carbonation and the beer is perfectly bottled.
I was considering a cheaper solution though, and saw this webpage:
I have found the ball valves for $7/20 here:
And, they'd be much less obtrusive and far cheaper.
Anyone ever try this?