Things You Must Have on the Boat
Computer printer/copier/scanner - needed to photo copy boat papers and passports for
officials, etc.  Bring extra ink cartridges and paper.

Boat stamp - Yes a hokey rubber stamp with your boat name and coast guard number or
some design, etc.  Also an ink pad for it.  This sounds stupid, but in the indian ocean and
middle east they want everything stamped and signed so you must have one.

Electronic charting/navigaton software - easy to find out here from other cruisers and it will
save your butt when you are missing a paper chart of a region.

Computer with DVD burner to backup computer files and make copies of various things...  
Also blank DVDs and tons of them.  CDs just don't hold enough these days.  Heck a digital
camera can fill a CD quickly if you take tons of photos.

Serious big anchor - I have gone through a CQR copy (never set in sand  and always laid
on its side), Delta "no" Set (does not work in mud), Brittany (great in sand only), and now
have a Manson Supreme (bugle style anchor).  I hear a spade works just as well, but not
the aluminum ones.  Anyway I can't stress this enough to get a good anchor and bigger
than you need with at least 200 feet of chain or maybe 300 if you can afford the weight.  If
you can really afford it consider stainless chain because it supposedly does not bunch up
under the windlass.  You most likely will be limited by what fits on your bow, but at least go
up one size from what they say is right for your boat.  That is if you want to sleep at anchor!  
Needless to say a good windlass will be worth the investment (I have a tigress and it has
worked fine so far knock on wood).

Dive gear and knowing how to use it - Even if you are not a diver there will be a time you
need to scrub the bottom, cut a rope off the prop, change a zinc, or free an anchor from
rocks or coral.  It is also great for checking your anchor or putting out another anchor in a
blow, etc.  Use it often or snorkel to check if your prop is loose!

Spares -  Tons of everything unless you hang out in places with marine stores.  Spare
engine throttle cables, water pumps, toilet spares, bolts, nuts, etc.  I even had an ocassion
recently to use the spare prop!  Yes those complex 3 blade folding props have a nasty habit
 of falling off sometimes so a spare prop of any sort (mine is a two blade fixed) can come in
handy.  At least I have two engines, but with only one this would be a scary thing to happen.
 Epoxy and fiberglass come in handy all the time.  Spare alternator, impellors, wire, you
name it.  The only time you can have too much spares is when your boat is overloaded (and
I might be pushing that a bit:).

Friends - Friends to visit and bring boat stuff for you.  Friends among other cruisers to help
you when things break, etc.  Out here Karma does play a factor so help others when you
can and it will come back to you when you need it.

More to come as I think of it.