My love for Classic Traveller is based on how easy it is to stick whatever you want in. Bend the system whatever way you want it is very hard to break. For my money you don't even have to stick with communication is limited to speed of travel. That would only mess you up if you used the Third Imperium setting. The 3I is not necessarily Classic Traveller. It doesn't even get a mention till the fourth book and even then it got a mention in one paragraph (I think.)
So a titling a list as 'Things They Left Out of CT' would be presumptuous and out of the 'do it your own damn self' spirit of the Old School. So here's a list of things I would like to add to CT for my game. Please note they heavily favor a space pirate theme for some reason.
1) Laser pistol: the laser carbine and rifle are near and dear to my heart as they both scream SF! However they can be a pain at times. How do you use them when you're wearing a back pack? Similarly sometimes you want a hand free and a weapon that says 'SF' in no uncertain terms. In fairness Loren Wiseman addressed this tweak quite eloquently in Journal of the Traveller's Aid Society (JTAS) #2. Thank you Mr. Wiseman.
2) Robots: robots, Robots, ROBOTS! I can see why they were left out of the core LBBs. this is my one major peeve with GDW. They took 6 more core books to address them and the book had it's share of contradictions, was overly complex and the 'bots were kind of boring. They needed a little more fiction than science in them. After all SF had already given us Robbie the Robot in Forbidden Planet (yeah I know alien tech but still.) Please note the crew in Forbidden Planet also had energy weapons for sidearms (see above.) I want robots with a little personality. is a robotic parrot too much to ask for? Note Robots were addressed in JTAS #2-4 by Marc W. Miller and Loren Wiseman. Like all good things Traveller you are left to fill in the details and color yourself.
3) Grapple guns: okay we have these now though they are kind of clunky. I'd like to see something more like Batman's gear. Note I said 'grapple' gun and mean it. A magnet on a line is just weak and some wiseass on the other ship might just degauss the ship's hull. A grapple gun would be excellent for crossing between ships in space, getting control of your actions in zero-gee and a thousand other actions that will have the player saying things like, "I have to roll WHAT? I just wanted to swing across the staging area while blazing away at the guards with my laser pistol while my trusty robot sidekick deactivates the defense systems." Okay they handled 'grapnel' guns in Challenge #38 by Robert Sprinkle. I don't have that issue, yet.
4) Uplifted apes: primates make everything better. Also monkeys and pirates go together. Just keep them away from the robots. I couldn't find anything about apes in Traveller although they do reference uplifted dolphins. Blue Max Studios does Ships of the Black Desert, a highly technical epic series set in a near future solar system that uses uplifted simians for crew. Also see Encounter Critical by S. John Ross for 'Planetary Apes' and real science!
5) Reaction drives: M-drives are indispensable for long distance space travel. They suck for threatening other ships. See the previous post on space piracy. There have to be some reaction drives left out there. Of course the authorities will likely take a dim view of private citizens torching the landscape and other ships. Pirates don't care. Please check out Winchell Chung's Atomic Rockets webpage (http://www.projectrho.com/public_html/rocket/). He presents info on reaction drives better than I cold in a hundred years.
6) Cybernetics: believe it or not there is a place for eyepatches even among space travelers. Mythbusters showed that placing a patch over one eye preserves your night vision. If you are suddenly plunged into darkness just whisk off the eyepatch to see the defense robot coming at you. Of course you can't just chuck the patch in a space helmet. Much better to have an artificial eye with an integral thermal sight. You can even look really cool posing with your robot parrot and simian bosun. You're all in one piece? Keep attacking merchant shipping ...
Please note that this blog does not condone space piracy. It does condone giving space pirates cool stuff for your player characters to loot.