GPS and Depth
There are tons of stuff out there. Kind of depends on what you want to budget for it. You can buy one of the little Hawkeye or similar depth finders for about 100 bucks. A 2 inch unit, with digital read out and depth alarm. Uniden sells one that is identical, and I would assume the same mfg. You can find a hand held GPS for about the same price. I had one of the Hawkeye's on a boat I just sold, and it worked well and was very dependable. I am personally partial to the Garmin GPS units. I have had extremely good service with them, and they seem to be more user friendly than some of the others. To move up a couple steps in price, some new Garmin chart plotters now have all the charts built in, and also some have depth as an option. I have one of the 498 models and absolutely love it. As with all other boat stuff, investigate, find what suits your needs at the price you want to pay.