Woody, my counsel would be somewhat the opposite of Eric's "kitchen sink" approach. Here are the key issues I would consider when making your decisions:
1. The Caribbean
is North America's backyard. There is no place I've been there (which is just about all of it...) from where you can't manage to contact a NA vendor, have something shipped in, and get it out of Customs
and to the boat. From some places, arranging this is easy (e.g. Trinidad) and even cheap
(PR and the USVI, with secure, cheap
Priority or Global Priority USPS service) while in other places it is frustrating and expensive...but it's do-able. At first blush, perhaps 'frustrating & expensive' sounds undesirable, but consider how much time & expense is involved in assembling a comprehensive collection of spares (vs. zeroing in on only specific items; see below). Also keep in mind that you will only use some of those spares, ever. Plus you must then find space for it all (which you'll need for things that will - guaranteed - save you money
; see below). And truth be told, you won't buy every spare recommended to you (there are more of us than you!) and so to some extent may STILL need to resupply from NA after your departure, anyway. No...for that cruising venue, I think the general rule
of thumb is to be selective, not inclusive.
2. Load up on consummables because a) you know you will use them, and b) they may not be readily at hand AND will be more costly, when you find them: fuel
filters; filters for your water system (you really should have a Seagull IV filter for the Caribbean); pre-filters if you carry a watermaker; you get the idea...
3. Do an honest assessment of your boat's critical systems, which I would list as rig, rudder, engine and - from a civilized lifestyle standpoint - DC electrics, fresh water, propane
toilet systems. First, if the engine is "venerable" but long of tooth, put the 'spares' money
into the engine *before* you leave: replace the water pump (always a dodgy component on older engines used hard), take down the #1 alternator
to the shop to disassemble, clean & service), ditto the start motor (along with an electrical check), replace all the cooling
and oil hoses plus belts, and you'll cure most potential ills and be benefitting from the expense involved during the run. Ditto the rig. Survey
system - carefully. Service
it where needed, replace what is worn (idler bushings, perhaps chain & wire) - again, put the money into the system, gaining reliability
& peace of mind, rather than stuffing something in your locker.
Re: the fresh water, head and propane systems, you can adopt 1 of 2 schools of thought: Either 1) you will instantly drop what else you are doing and repair a FW pump, rebuild the solenoid valve (Caribbean propane has lots of oil in it from worn compressors, which in turn plug
up the solenoid over time), or head pump when (not if) it's worn enough to fail...OR 2) you know you might not have the time or immediate inclination, in which case carry a full spare assembly (FW pump, Head pump assembly, fresh solenoid). You can mix this up, too - perhaps the FW pump is too expensive, so you choose a rebuild kit instead. I don't know many crews who want to live without their pressure water system, head & stove, so be realistic about which approach is for you.
Re: DC system, most of that won't wear. However, I would recommend carrying a spare alternator that you install and trial run before leaving, then cushion, bag and seal up.
Overall, the point of #3 is to prioritize what you really don't want to live without on YOUR boat, AND what you know will be heavily used. Then zero in on those items, replace what is dodgy, old or worrisome up front and carry the rest.
4. While coming S and then leaving NA, keep in the back of your mind that Puerto Rico
is you 'real' stepping off point re: logistics. 800#s work, the island has every vendor needed, USPS is reliable and takes only 1 extra day for every kind of service
, and things aren't that much more expensive there (unlike much of the E Caribbean). Keep a little list going as you realize you forgot something or you're burning thru filters faster than expected. When you get to PR, hit the NAPA store and check off all the other things on your list...and at the same time, stop and enjoy a great cruising venue that most N Americans fail to enjoy.