Even on a three day trip, I'm still a one-take Jake. Roller dive bag, cylinder, small overnighter. All carried in one trip. During the days, I'm in my suit, at nights its shorts or sweats. Some stuff to remember:
#1 - a big insulated mug. Most big boats have a soda gun, and expect you to use those limp styro cups. Put your name on it and use it for 3 days. Get real. Bring a big ol' insulated mug, fill it with ice and let the diet pepsi flow, baby.
#2 - fully stocked dry box. I have my mini box for 2 dayers and Catalina trips, and a bigger version for the multi's - difference being hoses, drysuit repair kit, spare second stage and some other stuff. Saved my trips a time or two...but it saves someone elses on every trip I've been on.
#3 - SUNSCREEN - can't pull chicks with lobster face. OK... I can't even say that without slapping myself. Don't get burned.
#4 - Homeward duds. Frank is on the money... a soggy drive home is below average. Big 2 gallon ziplock with spare shorts and spare tee. The rest of the clothes I'll roll through, as well.
#5 - MY PILLOW. Call me a sissy, but there is no pillow like my own. So I always bring it on these trips.
#6 - Always bring a penlight. I always bring a travel alarm, too. Bonine can knock me out, and I never miss a dive.
#7 - Water. I bring 2 liters for each day. Pound it between dives. Diet Pepsi rules, but my body needs water.
OPTIONAL
* Cash - there is usually a poker game one night. If not, I'll get one going. I need enough to get in the game so I can take everyone elses casheesh
* Leaf - nothing beats a fine handrolled under the stars on the top deck. My fav time of the trip.
* Drysuit hanger - most big boats have a place to hang your suit inside out between dives / overnight. HINT: throw a deckhand a fiver and ask him to hang your suit below deck in the engine room. Its warm, dry and in the AM you'll have the only dry suit in the place
* Big clamp - I bring one of those giant clothes pin-looking metal carpenters clamps. Great for clamping my drysuit undies or towel to the rail as we move from site to site. While other peoples towels blow into the ocean (and they will) your's will stay put until you need it.
I'm completely jealous of your trip. If you need a stow-away, I'm there! Enjoy.
K