Gear that you need as crew, assuming that you are not racing but making longer bluewater passages, working as crew:
Personal PFD with Harness
If an inflatable, at least two spare inflation kits. Should have a whistle and strobe on it as well. If you carry a
rigging knife, you don't need one on the
harness. Be aware that different airlines have different requirements for carrying inflatable PFD and CO2 cartridges. Mine is a Spinlock Deckware Pro
Harness with PFD.
Safety tether
I prefer an ORC-approved one with two legs, safety clips on the two boat ends, and a snap
shackle on the body end.
Rigging knife
I carry and use two different ones, a Leatherman Charge multi-tool and a Boye's
Rigging Knife.
Flashlight—
I like the LED-based one, since they're often brighter with longer battery life than regular ones. I keep the Energizer Lithium AA batteries in it... since they're both lighter and longer lasting.
Binoculars and/or hand-bearing compass
The handbearing
compass is an Iris 50, and the binocs are 8x30 Steiners
Personal handheld GPS
A
Garmin 76CS. I like keeping a track of where I've been/gone. It also provides a quick and dirty backup to the boat's main
GPS in a pinch.
Good foul weather gear
Should be appropriate to the season and area of sailing, as well as they type of sailing you're doing.
Personal Journal
While not a necessity, not a bad idea IMHO. I carry and use Moleskine notebooks. Carry a Fisher Bullet Space Pen to write with.
Passport and other travel documentation
I carry mine in an anti-theft wallet.
iPod and charger
Looking to get a small solar charger for it, but can charge off of any 12V system or USB port.
Digital camera and charger
The one I carry is an older Pentax Optio WP, and is water-resistant. Unfortunately, the charger is only 110 VAC IIRC.
Travasak or sleep sack.
The one I have is made from micro-fiber cloth, rather than silk, since it is much lower maintenance.
Small personalized first aid kit
Should contain any prescription medication needed for yourself, as well as things like sunscreen, vitamins, etc.
A good hat
I wear a Tilley Hat.
Good sunglasses
Mine are prescription and custom made, with polarized clip-ons.
Good sailing gloves
I will carry at least two pairs, depending on where we're sailing
Good deck shoes
There are lots of ways to injure your feet on a boat, especially one you don't know very well.
As for quantity and type of clothing, that's really kind of a personal choice. If you don't mind doing laundry often, bring fewer clothes. I generally pack a variety of versatile clothes, since I know that conditions can vary a lot over the course of a passage. The pants I carry are usually Mountain Hardwear convertibles, so that they can be worn as shorts or as pants. They're synthetic and wear like iron.
Even in the Caribbean, I'll usually have at least one fleece long-sleeve shirt, since they're light, warm, and very low maintenance.
I'd avoid cotton clothes, since they're quite prone to mildew, don't dry quickly, and provide almost no UV protection once wet. Almost all of the clothes I carry while sailing are synthetics that are designed to keep you warm when wet, dry really quickly, or both. Fleece falls into that last category.
All of this stuff fits into a large drybag, and much is packed in smaller bags inside, to help keep things organized.
I hope this helps. Some people think that some of this stuff, like the PFD and
Harness should be provided by the boat and captain... In an emergency, do you really want to trust gear that you don't know, aren't familiar with, and aren't sure what condition they're in??? I wouldn't... so I carry my own personal gear.