For a cold weather voyage of a week, this is what I would recommend:

sleeping bag
2 pair jeans (with lycra to allow greater freedom of movement) *note: I like jeans, but some people prefer quick-drying cotton trousers. I find that if you have a good set of waterproofs, you don't have to worry about your jeans getting wet.
5 t shirts
2 sweat shirts
1 pair thermal (top and bottom)
warm gloves (when not on duty)
wool hat
gortex waterproof jacket with zip in linings (I bought an excellent all-weather jacket from LLBean with a zip-in polartek lining as well as a zip-in primaloft lining)
plenty of socks and underwear
ear plugs
walkman (with a relaxation tape to help you to sleep)
eye shades
night clothes (sweats will do)
pillow case
1 big towel
waterproof watch
chocolate (for those long nights on watch)
sea sickness pills (I found Bonnine works the best)
sea bands
candied ginger (yet another seasick remedy)
camera with lots of film
disposable waterproof camera
travel diary and pen
running shoes
sturdy rubber souled boots for working aloft
shampoo, toothbrush, toothpaste, and other toiletries
Wet Ones towelettes in foil packets
large zip lock bags to put your dirty and wet clothes in
clothes line
band aids
RYA logbook or ASTA logbook (if held)
nylon pack for shore excursions
credit card and pocket money
passport (if going to foreign ports)
knife and marlinspike (beginners need not worry about these)

*check to see if seaboots and oilies (waterproofs) are provided.