Optio equipment

[Felix Canus]

Isn't there some evidence that the legionaries of a contubernia would buy a sort of "common slave" for the unit? You know, for the upkeep of equipment and the cooking of food and such?...

There seems to be an argument whether or not the contubernia's calo was a slave or not, and that may have varied, but you are right that there was apparently a non-soldier in that position. But I am under the impression he was assigned to the contubernia rather than purchased directly by the soldiers. Again, this might vary, but I don't think the soldiers could have afforded to buy a reliable semi-skilled Latin-speaking slave on soldier pay.