I cruised and lived aboard full time for several years on a Hatteras 56MY. The old saying "The definition of cruising: working on and fixing your boat in exotic places" is so true. Here's a list of my MVPs, or MVTs if you will (spare parts is another story), not mentioned already in most cases. I had one of those Craftsman sets, maybe 150 piece. I got something out of there maybe once or twice a year. By far the most used wrenches on the boat was a set of stubby Gear Wrenches, a ton of uses and gets into places where a normal wrench or ratchet set either doesn't fit or takes forever to get anything on or off. Also heavily used was a set of T nut drivers and T allen head driver, as well as a full set of allen wrenches. The nut drivers also got into hard to reach places and are very handy for hose clamps. Remember to have a 7mm for use on AWAB clamps, by far the best hose clamp for applications that don't require a T bolt type. A ratcheting screw driver with a variety of ends is likewise invaluable for places a drill driver won't get into. Speaking of which, smaller is better on the drill driver. Rubber mallet. A small wet/dry vac, say a couple or three gallons, something you can carry around easily and get into tight spaces. One of those long skinny springy "grabber" devices; everything you drop will find its way into an otherwise impossible to reach cranny. In the same vein, a small mirror on a telescoping rod. Tripod style flashlights. A headlamp. One of those bigger plastic floating flashlights with foldable handle. An LED long skinny trouble light. These make use of your tools possible in many cases, and much more efficient many more times. It's been mentioned, but the best small digital clamp on multi-meter you can get. Absolutely essential. A few sets of various lengths of small jumpers with alligator clips on each end. When you need one, it is invaluable. Also as mentioned a good set of ratchet crimpers, practice using them in advance. A variable heat gun with various ends to it, especially the curved type for heat shrink. Many uses for this. Various types of sandpaper and abrasives. I found one of those tearable 1" rolls of abrasive tape very handy in particular over the years. Vaseline and Corrosion X. Antiseptic cream and Band Aids.