|The big black things do not appear to be functioning cannons.|
Instead, I've gone with Slicing - an odd gathering skill that does very little for crafting but does find literal safes full of credits scattered around the landscape. There are also slicing missions and I've had extremely mixed luck with these, generally breaking even. (I've heard these were more lucrative in previous patches.) While I suppose it's hard to complain about breaking even while earning skill points, in general I'm sticking to the guaranteed returns of looting lock boxes.
Meanwhile, my other two slots are occupied with the Biochem crafting skill and Bioanalysis gathering skill. Bioanalysis produces all the materials I need to make common medpacks (potions) and stims (longer stat buffs) with Biochem. There are some NPC costs associated with training and materials, but in general this is a very low cost way to obtain all of my consumables. So, I'm basically getting everything my character needs and operating at a net profit from crewskills alone, which makes all of my quest rewards and drops pure profit.
I hear mixed things about the other crew skills, and I can't make use of any rare recipes I learn through reverse engineering (a process in which crafters are reimbursed for destroying the common items they make for skill points) for lack of the associated mission skill. That said, I would not hesitate to recommend this particular combination to any other newbies looking to purchase their first speeder.