Lots of talk of this forum about electronics, but not much mention of all the apps that you can get for free on your smart phone.
GPS plotter (several locations available); actually works as good as anything, has tides, keeps track of routes, waypoints, etc, available for lakes too! Worked great in Seward last year!
Marine Weather bouys; Faster than messing with computer, great for checking obssesively all day, has all the bouys we use here, tides also.
Compass (that's really common...)
The one that I thought was really interesting is the "range finder" app. It comes as a set, "Smart Tools" has about five different tools in the one app. I use it to anchor in tight coves, gives me a better idea how close I am to the shore or cliffs. Usually when you leave in your dinghy you realize you could have anchored closer!
I usually throw my phone in a ziploc then in a drawer for the trip (the whole point of boating- "unplug") but I have two GPS on my boat and needed one for back up once during an electrical hiccup. If you only have one, but have a phone that phone might be your back up.
Anyone else loaded with boating apps on your phone or know of any that I haven't mentioned?