For those who are unfamiliar with the historical facts of the Caribbean in the 17th and 18th Century, or would like to get a feel for the atmosphere of the campaign, here are a few suggested sources in relative order of usefullness:
On Stranger Tides by Tim Powers, Novel
Great read and the original inspiration of the authors of the Skull and Bones sourcebook.
Time Life Books Series The Pirates by Douglas Botting, Non-Fiction
Great 'coffee table' book put out many years ago. Most libraries should have it and it is probably available on e-bay or Amazon.
Disney's Return to Treasure Island, TV Miniseries
Only available on DVD from the UK, and you need a British DVD player, but you can find the entire series on You-Tube. The quality is poor but the story is phenomenal swashbuckling goodness. It has it all; mysterious islands, shipboard fighting, pirates, smuggling, cruel villains, treachery, mutiny and of course treasure.
Under the Black Flag, The romance and reality of life among the pirates by David Cordingly, Non-Fiction
Generally regarded as the best modern source for historical information on piracy in the Caribbean. Scholarly, but not a dry read at all.
The Republic of Pirates by Colin Woodard, Non-Fiction
Another decent historical account of piracy, focusing on several pirate captains that operated in the northern Caribbean in the time period just a few years after where the campaign will start.
The Pirate Primer by George Choundas, Lexicon
This guy scoured every source of pirate language, from historical documents, film, TV and literature. He then created a Pirate lexicon with dictionary-like entries explaining pirate speech. A suprisingly scholarly work. Very comprehensive and full of little bits of immersion.