Lots of good advice here. To sum up (and put my spin on it)
- any good boat chandlery
(online or brick) will have panel mounting 12v cigarette lighter sockets. This one is available most places
, and is good quality. Get two.
- Install them in your boat, with each fed from its own 10A breaker or fuse. Use #14 marine-grade wire if the run is no more than 20 ft from the plug to the panel (for max 10% v drop @ 10A, as per ABYC)
Now you have two 12v sockets capable of driving most typical portable 12v items of up to 10A each.
- buy one or two cigarette lighter-to-USB adaptor things
. They are available just about everywhere for under $10 typically. Ours have two USB jacks and a sexy blue LED
- optionally buy a 75w or 100w plug-in inverter
(usually under $30) for the occasional time you need to power a small
AC electronic device, like a laptop's AC power supply.