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.