Most necessities are provided by the ship but a few amenities can make the cruise more comfortable:

Sea sickness medication:  If you know you are prone to seasickness, bring any medication you know works for you. Marezine, Meclizine, Bonine, Dramamine or Scopolamine anti-seasick medications are some examples – some work for some people; some have side effects; some dosages require a prescription. The ship can provide over-the-counter remedies but we suggest consulting your doctor or pharmacist & bringing your own. Summer and fall cruises are typically calm but the weather can get rough any time of year.
Clothes you can layer:  It is better to wear multiple layers than wear a heavy jacket since you will be moving in and out of the climate-controlled lab. Even summer cruises can be cool (even cold) so always bring long pants, a windbreaker, sweater or sweatshirt, and a beanie.
Boots:  Calf high rubber boots are a must-have.  The work area is usually swamped by seawater so your shoes will constantly be wet. Comfortable, waterproof boots are a necessity since you will be sampling from the CTD or washing nets. The more comfortable the better but even cheap ones are better than wet tennies. We have a limited supply of 'loaners' sizes available upon request.
Alarm clock:  Necessary. A cell phone (on airplane mode because of loss of signal or changing time zones) may be good enough. 
Hard hat:  NOAA & SIO vessels require hardhats during loading and while working on deck. The ship will provide one but bring one if you prefer your own.
Closed toed footwear:  These are mandatory while working on-deck and any general work areas. Steel-toed shoes/boots provide extra protection so are highly recommended.
Rain gear:  Foul-weather jacket and pants are worth taking along. We can provide a few pairs but sizes vary so if you have something waterproof, bring it.
Sun protection:  Sunglasses, a hat, sunscreen and Chap Stick – you can minimize your sun exposure but these are worth bringing.
Toiletries and medications:  The ship provides linens and bath towels, but bring your own personal hygiene products (shampoo, soap, decongestant, Advil, etc). The ship is relatively small so consider bathing regularly a courtesy to other people.
Shower robe / shoes:  Makes getting to and from the head (bathroom) more convenient.
Workout clothes / gear:  A stationary bike, stair-stepper, mat, and bench/free weights are available.
Books /magazines / music:  The ship has a magazine & paperback library plus movies but the selection can vary.
Binoculars / camera:  Sightings of birds and marine mammals such as seals, whales or porpoises are common on CalCOFI.
Snacks and goodies:  Some ships provide lots of these but if you are particular, bring it. Midnight watch-standers often bring soups; canned tuna and staple food items since meals are not serve from 6pm to 730am. There are sandwich fixings, cereals, dinner leftovers or you can request a plate of food from dinner be saved. If you have any dietary restrictions (allergies, gluten, vegetarian or vegan) please let the volunteer coordinator & cooks know.
Clothes for a week or more:  Laundry facilities are available but the washing machine will be unavailable during rough weather so plan accordingly for 16 days.
Fishing pole:  Trolling for albacore & bottom-fishing are common, especially summer and fall, so if you like fishing and have a sturdy pole and tackle, bring them.
Soft luggage:  We recommend using soft luggage to stow your clothes and other personal gear such as a duffle bag or backpack since hard suitcases will not stow easily into your stateroom closet/locker.