Unlike my B/X stuff, I still have the box that my Classic Traveller set came in. It’s beat to hell and held together with silver duct tape, but it still holds everything I ever owned for the grandaddy of science fiction RPGs.
Though the Little Black Books aren’t really all that photogenic, I have always adored the simplicity of their graphic design.
I never really messed around with any of the books after 1-3, though I did own Mercenary and High Guard. Citizens of the Imperium was my absolute favorite supplement, and the Paranoia Press Scouts & Assassins got a fair amount of use in my games, mostly owing to the Martial Arts rules contained within. Supplement 1 was always good for grabbing an NPC or two from when needed.
I had one official adventure (the double-adventure Marooned/Marooned Alone) and the book of adventure seeds known as 76 Patrons, though I never really used either. Homebrewed settings and adventures have been my focus pretty much from day 1 of my gaming life.