Re: Your sailing "must have".
Especially for solo offshore....
harness, tether, jacklines, means to re-board
some easy furling arrangement for the main
dinghy or life raft with a real, floating ditch bag and emergency supplies, not just the minimal stuff that might be in the raft
passport, copy of passport main page hidden away safe, phrasebook, crew list
customized 1st aid kit, meds, prescriptions, sunscreen, meat tenderizer, syrup of ipecac, activated charcoal
sail mending stuff -- needles, uv-resistant thread, palm, sewing awl, patches, tape, etc.
spare shackles, clevis pins, ring dings, maybe a couple of blocks/snatch blocks, etc.
clean fuel tanks/polish fuel/replace old fill tube gaskets before big voyage
spare bits of line, duct tape, sandpaper included with spares and tools mentioned by previous posters
mask, snorkel, fins, probably wet suit and stuff for going in water if needed to clear prop etc.
wood plugs, stuff to stop leaks
gel coat patching stuff, disposable gloves, plastic film
comfortable pfds/inflatables, float coat for cold weather, whistle & light attached
comfortable breathable foulies that keep (most of) the wet stuff out
courtesy flags/q flag/ensign if abroad, yc burgee if visiting ycs
pepper, garlic, spices
head rebuild/fix-it parts
spare "key" or rigging knife able to open deck fills