For trailers, a large grease gun loaded with whatever marine grease is available. You'll go through a lot, so its not worth it imho to spend $$ on synthetics. A nitrile glove is the perfect thing to keep the grease from getting everywhere. Not on your hand, but on the gun tip.
For the engine, a small, spring-loaded gun with good quality synthetic OB marine grease. As already said, US OB MFR's sell it for a lot less than some of the Japanese OB MFR's, including yamaha and honda. Same with fuel filters and fittings. A filter for a yamaha F250 is the same as the suzuki F200, but costs 2-3x more. The Mercury version is a buck less than the 'Zuke.