For the last Traveller campaign I ran, the PCs were the command crew for an Imperial supply ship, doing a 'milk run' visiting worlds along the Spinward Marches/Trojan reach border. They had various cargoes and packages to deliver to allied governments, Imperial embassies, military outposts and colony worlds, or to pick up and bring back.
I don't have the design to hand, but the ship was an old TL 13 design, due to be decommissioned after this last run. I can't remember the exact displacement, I think it was 800 dtons. It carried a modular cutter, two 10 dton fighters and well over 100 dtons cargo capacity.
It was a fun campaign, they got involved in a variety of diplomatic incidents, encounters and such. In one scenario they arrived at a colony world just before an Ihatei fleet, and got caught up in negotiations and conflict between the colonists and Aslan.
They carried a sealed cutter module with instructions to deposit it at a particular location on a planet at a particular time and enter an activation code. The module contained a grav APC and a special forces strike team in low berths, with instructions to assault the residence of a merchant known to be financing piratical and terrorist activity. Their job was to kidnap him or the most senior personnel at the residence and capture whatever incriminating evidence and intel they could. I handed the players pre-genned stats for the strike team and had them play through the misison, then switch back to their main characters to extract them off the planet.
It was very episodic, with a few common threads running through the campaign.
Simon Hibbs