Buying ahead can help future cruisers score big bargains, or at least avoid paying full retail in the frantic months prior to departure. It's highly unlikely that higher value items that aren't installed/wired into the boat will be included in a purchase, so this is the perfect category to scope. What have we found most useful that fits into that description?
Handheld boat equipment
VHF. You may not realize it now, but your life will be coordinated by VHF. I consider two handheld units to be a practical minimum, so you have a backup when (not if) your primary fails you in an inconvenient location (ours chose Tonga). If you have a family, consider having more so you can keep track of children.
Omnipresent VHF clipped in for an early morning hike: Agua Verde, Mexico.
GPS. Let's face it. We have fun practicing with a sextant, but we are not going to use it in more than a novelty and educational capacity. There: I said it. Having multiple backup GPS units is good. Besides backing up (in multiple...at least two) the possibility of failure with our primary GPS on board, they're fun. We've been geocaching in Mexico with the Don Quixotes, and it was a blast. A handheld can be handy for land-based travels, too: that path up the volcano seems really obvious on the way up, but perhaps not so obvious on the way down.
Night vision monocle. The use may seem too small to bother with, but it can be indispensable at times of stress for understanding what is around you. At those times, whatever it costs feels like enough...better yet, source with patience and a discount.
Other handheld equipment that we don't have on board (but wish we did): these qualify as very nice boat jewelry that I would love to have scored a deal on before we left. My opinion isn't quite based on direct experience, but 20/20 hindsight.
Satellite phone. To date, we have been 100% radio centric. I still expect to be radio centric in our cruising communication, but having had our SSB fail- not once, but twice, at critical points in our Pacific crossing- I want backup. It would have been stupidly expensive to source a sat phone in the islands. We expect to have one on board when we leave Australia.
Range finder. How many times have we been at anchor in a blow and thought...I wonder how close we're getting to that cliff? I'll tell you: ENOUGH! Once would probably be enough, frankly. And it's been more than once. I am debating one of these for Jamie's birthday... ssshhhhh... maybe he won't read this far.
Handheld watermaker. This is a high-end ditch kit item, the kind of thing you never hope to need. Yes, we could build a solar still and yes, we hope we never need to. But if we hadn't been hemorraging money just before we cut the docklines, we would have gotten one. And then there was that day, a week out of Mexico heading for the Marquesas, when our watermaker failed and contaminated every drop in our tanks. We had nearly two weeks until landfall, and that day would have been a lot less stressful with a backup aboard.
Personal electronics
eReaders for everybody! We now have five of these on board, because we couldn't share. Totem has a mix of nooks and Kindles, but frankly, I don't think the brand matters as long as 1) it is e-ink based (not backlit, like a tablet: power pig, harder on eyes, and not so hot in bright sunlight) and 2) it can read the popular ePub file format. That describes almost every ereader on the market.
Tablet- iPad or Android. Yes, in addition to the ereaders. No, we are not digital junkies. Honestly? We haven't crossed this bridge yet and are getting by fine, but like the sat phone- we won't leave Australia without one (and probably two) on board. I'm leaning towards Android. It would be good enough as a media device, but they offer benefits for navigation as well - thank you, Navionics. I'm convinced that we could have navigated better through the reefs in Fiji with a tablet than we did with our sets of (extremely inaccurate) paper charts plus chartplotter.
Cameras. Even if you're not a big shutterbug, you'll probably want good images of your travels. If you are a serious photo fiend, get a nice DSLR. We didn't get one until after Year 2 (thanks to my awesome brother. Very timely that he was expecting a kid and decided to upgrade, and passed us his old Nikon body). Also- at least one underwater camera, for a few reasons. The basic one is that they are the ultimate durable pocket-sized camera: they won’t die when (again, not if) the dinghy flips, and they will help you remember those pretty fish you saw so you can ID them when you're back on the boat. Besides, they just keep getting more affordable. We had a cr@ppy camera that made it only about one year (possibly because it had a 3 meter rating, but I routinely snorkeled with it to 6+ meters), but it's easy to find cameras rated to 10 meters now. I'd shop for this, but not buy until you know you're in the home stretch- technology just changes too quickly. I've got my eye on this nice Lumix.
Some of our best memories are captured by basic point-n-shoot underwater camera. Vava'u, Tonga.
Personal gear / soft stuff
Foul weather gear. Good gear is stupidly expensive. It's also an excellent item to score on eBay. We have foulies (and backups / crew spares) purchased for a fraction of retail. My best score was a top end Henri Lloyd jacket for Jamie, $800 tags still attached, <$200 on eBay. That said, these just don’t get worn very much in lower latitudes… but when you need them… they are worth their weight in gold.
Sun protective clothing. In lower latitudes, the fancypants SPF rated stuff does make a difference. If you are super white, and genetically disposed to melanoma like us, it's important to take seriously. Big hats, swimming skins, and ventilated clothes with good protection values are worth it...and, expensive at retail. Solumbra and Coolibar are good providers... I personally troll the semi-annual Patagonia sales.
Niall and Mairen sporting serious sun protection. Isla Isabel, Mexico.
First books... then personal gear... up next in the ruminations on useful cruising "stuff" you can source in advance: the fun stuff.