There's nothing worse than getting all psyched for a day sailing, (or a race) and then a small item breaks or is lost and prevents it.

Has anybody compiled a list of "essential" spares for the Nacra F18?

Is F18 a class which has more boats, or do people just say F18, when they mean the Nacra?

Your spares list will depend on how hard you race...

Start with some rope of various sizes, an assortment of shackles and a single block. beyond that you start getting expensive.

There are a lot of different F18 designs. For more info try here

When you get serious, spares of these

Sails

battens
spinnaker pole
tiller extension
tiller cross bar
smart ratchet
trap and stay wires

mast

what is a smart ratchet? Where would you recommend purchasing the parts you mention?

a spare dagger board and a spare rudder are a nice have also. I just lost a weekend of sailing due to a broken dagger.

Depends on how much you value your sailing.

serious = full spare boat (been there done that)

Missing from the list so far:
Rudder arms
5mm shock cord (bungee)
lengths of various ropes
spare hatch covers (in case they are "borrowed")
plenty of spares screws, nuts and bolts, rivets, pins.
I keep a number of split rings on my car key ring, they are so easy to lose at the beach.
some solid stainless steal wire.
spare cleats.
you could go in for a dolphin striker but if that breaks your in for more repairs than you will manage at the beach.
some small pullies, 29mm and 40mm singles.
Depending on your arangment for hooking the sail onto the top of the mast, spare hook/ring
spare boom section


Like I said, it just depends on how keen you are!

after de-masting in the gulf of mexico last summer, i now sail with a watertight container with parts.

This includes:
a few misc bolts and few misc screws
a few pins and ringdings
screwdrivers
a small ratchet driver and 2 common bolt size ratchets
knife
a shackle
misc lines
spare car key
very small bottle of sillicone.
some sail repair tape
and a tube of 2 part pool epoxy - to repair holes in my hulls. This has allowed me to sail 6 miles back to shore (after draining) with a hole that filled my hull in a few minutes.

I also carry a small homemade medical kit, with lots of bandaids, sterile gloves, ace bandage, asprin, hydrogen peroxide and bactine (I SUFFERED) WITH 2 infections last summer from sailing related cuts that could have become REAL serious...

I realize this is a bit overkill... but i would rather carry an extra 3lbs of gear than not have ANY of these items when push comes to shove.

as far as spare parts goes... I sail a Mystere, and parts are semi hard to find.. and seem to be fragile so i just purchased a set of upper rudder castings after finding a crack in my originals. I figured i would change out to new ones.. and have a spare. I also have a spare set of rudders. I broke a few cheap pair on my TheMightyHobie18 and figured i would buy these while they were around. Also i have a spare tiller extention in my sailtube...

I wish i had a set of high wind pintop sails to go out in 25knot days with less power.