When we started our cruise I was pretty skimpy in what I took, now (five years later and half way around), I have just about everything - more stuff than I used to have in my kitchen back home. You can ALWAYS find the space
One thing that helps for space is if there a place that you can build a spice-rack. Pick some decent (and nice looking) clear spice jars and build a spice rack to fit them. The spices look good and are easily accessed, and free up a cupboard. Also, if you sink is next to a bulkhead consider mounting a dish rack ... it will drain into the sink and then you won't have to hand dry your dishes or have them on the counter (granted you can't use the rack in rough seas, but who does dishes when it's rough out anyway??)
My vote is FOR the pressure cooker. I got one that has two size pots (one lid). The pots are great for general usage, and the large pot doubles for lobsters, pasta, and such and for a deep pot when at sea and I don't want to worry about stuff spilling. Other pots/pans can usually fit inside the pressure cooker pot(s) and you can get a dual pressure set that nests with itself - so I don't think you are looking at a lot of room. I then also have the strainer basket that fits in one of the pots for pasta (therefore no pouring boiling liquid out at sea as another post pointed out).
The Evergreen bags DO indeed work (I actually did a test with carrots). I don't think the Glad green bags work as well as the Evergreen (again another real test). They say to use the Evergreen bags in the refrig, but I don't refrigerator most of my veggies.
Carry a knife sharpener ... no matter how good your knives are, they will go dull.
For bakeware the silicon stuff is GREAT. As pointed out, no rust, no breaking, easy to wash.
Rubbermaid (and others I'm sure) now make collapsible tupperware - they collapse down with the lid on into very slim pieces ... I departed before these were out and haven't found them abroad, but keep looking as my tupperware storage bin it full and a mess.
I also recommend Bar Keeper's Friend ... it's great for getting rust out.
I've got some other tips here
and more details on the above tips (including a photograph of the dish rack).