As I said in another post, discovering the Traveller Starter Set is available for free yesterday convinced me to look around and see what other interesting Traveller goodies might be available. GDW is offering almost everything they published for Classic Traveller in PDF at very low prices. All 13 Supplements are available. Here is a list of the ones I consider almost essential to running a sandbox-style SF campaign with Traveller:
Supplement 1 - 1001 Characters Currently $2.00
"Contains 1001 pre-generated Traveller characters ready for use as non-player characters, quick characters for a spur-of-the-moment game, or to supplement the work of the referee. Plus a bonus of nine characters drawn from science-fiction. 44 pages." This sounds like a boring book and it is boring to read. However, it is great when you need an NPC on the fly. All the characters have stats, skills, and are ready to use. I used my print copy in just about every Traveller game I've ever run.
Supplement 2 - Animal Encounters Currently $2.00
"This supplement provides a general set of animal encounter tables for use in most common situations. 48 pages." Like Supplement 2, Animal Encounters is just as boring to read as it sounds. Given how much of a pain it can be to create an animal for an encounter on the fly in Traveller, it's one of the most useful supplements GDW published for Traveller, especially if you run a sandbox style campaign instead of running pre-written adventures. Like 1001 Characters, I've used this supplement in just about every Traveller session I've ran over the years.
Supplement 4 - Citizens of the Imperium Currently $2.00
"Character generation for twelve new character types. Wet Navy, Orbital Forces, Barbarians, Belters, and more. Plus 40 pre-generated examples of each. 48 pages." This supplement fleshes out the "Other" character type for player characters and the 40 pregens for each type are every bit as useful as the ones in 1001 Characters. Complete character generation tables are included for Pirate, Belter, Surface Navy, Diplomat, Docter, Flyer, Barbarian, Bureaucrat, Rogue, Noble, Scientist, and Hunter character types.
Supplement 6 - 76 Patrons Currently $2.00
"Sixty separate patron encounter situations for everyone from a single adventurer to a dozen or more, each one with three or more possible resolutions. Plus 16 mercenary job offers. 48 pages." This supplement is great for creating patron encounters and the adventures taking a patron up on his offer might generate. Just flipping though the book generates ideas for adventures. While this book is somewhat less essential than others on this list, it's still a book I would not want to try to run a Traveller sandbox campaign without.
Supplement 7 - Traders and Gunboats Currently $2.00
"Detailed deck plans for common starships within and without the Imperium. Plus, High Guard statistics for each starship. 48 pages." This supplement includes plans and details for Scouts, Subsidized Merchants, Free Traders, Close Escorts, System Defense Boats, Xpress Boats, and small craft. You probably could live without it, but it makes it far easier for you and your players to use common ships in your adventures.
Most of the other supplements are less useful as they are either something most campaigns will not need (Supplement 9 - Fighting Ships, for example, is full of High Guard stats for huge naval vessels) or only useful in campaigns set in GDW's Third Imperium. One of these other supplements probably is worth the money, however. Supplement 3 - The Spinward Marches details the Spinward Marches sector which is the home for most of the adventures GDW published for Classic Traveller.