Although the economy of the Imperium is largely based on what can be torn from the ocean, the piratical nature of said economy allows a wide variety of food and drink to be available, given the often exotic nature of targetted ships.
The most popular dish amongst the working corsairs of the Imperium is Epic Mouthful, a stew with a name as interesting and difficult to explain as the stew itself. Usually shortened to "Ep'mo" by the corsair on the go, this hearty concoction contains all of the proteins, fibers, and grits that make pirate life so enjoyable. It is a healthy mix of roots, meats, and so forth, coupled with congealed fat. It makes the mouth stick shut, and coats the stomach nicely, thus enabling the truly adventurous corsair to partake of that old nautical standby, Grog.
Grog, as it is affectionately known, is a bilious beverage that has amused and concussed corsairs for generations. It is a dreadful brew, synthesized from the water that congeals under sodden grains, the leftover tar at the docks, and one part per hundred pure whisky. It is left in a brass cistern until it corrodes, at which point the concoction drops slowly into a lead vat below. The liquid is packaged in a tombstone like wafer, and distributed to the ships. One jug, at roughly three gallons, will sustain a ship for four months, barring any unforeseen revelry.
Within the civilian sector of the Imperium, different tastes can be found. Most of the landlocked workers enjoy simpler, less violent fare, such as cereals and wine. This sends waves of mirth cascading through the corsair ranks, as it is their very pirating that provides this bland food for the civilians. The corsairs reason that they have complete control over the eating habits of the Imperium, and, were they to modify said habits, they would be able to have even the Emperor on an all-seaweed diet before the year was out. Corsairs are not known for their practicality.
The system of islands that are home to the Imperium are not, in any sense of the word, verdant. They are not lush, except in coastal trees and shrubs, and they are certainly not fertile. A simpler way of putting all this is that they can't grow much of anything there. Actually, that is not technically accurate. Several of the outlying islands are hospitable to certain crops, but not ones that one would be joyful to eat.
There are many fine restaurants in the Imperium (Sconner's Crab Shack, Royson St. James' Established Eaterie and Taxidermist, Such'n'suches), and even a few externally. Several enterprising corsairs have realized that there is money to be had in the catering business, and, as such, have transformed their gnatty old barques into seabound domiciles of haute cuisine. These restaurant ships ceaselessly patrol Bully Harbour, attaching themselves to any new ship that comes in. Most corsairs, after several months at sea, will be glad of fresh, steaming hot alternative to hardtack biscuits and pemmican, no matter what that alternative might be. Indeed, one of the most successful nautical restauranteurs is Jingo Smyth, owner, proprietor, and sole employee of Smyth's Halfway Cabbage Haus. Having discovered that what the hungry corsair wants more than anything is to eliminate the taste of dust and scurvy from his parched mouth, the wily Smyth brought to bear his unequalled knowledge of the preparation of the cabbage, a vegetable that was very unpopular on the shore, given that there were, at any given time, at least a hundred better tasting options available. The first taste of home for many a corsair has been Smyth's fabled (not to say legendary) Cabbage Surprise, a sort of featureless paste that tastes almost entirely, but not quite, unlike anything else. Fortified with vast legions of essential vitamins and nutrients, the Surprise always goes down easy. It often comes up in much the same way.
Although the culinary situation may seem quite dire, it is hardly as dreadful as it appears. There is an abundance of fresh fish, potatoes, bread, and cheese to be had both on and off shore, provided that one moves in circles exalted enough to be privy to such sweet foodstuffs.