Pugio

Just in Case
The pugio was a Roman military dagger, usually worn on the belt. Much smaller than the gladius, but not an afterthought: some surviving examples have beautifully decorated scabbards and fittings.
In battle it was a backup, for when something happened to the sword or the fighting got too close for comfort. Around camp, a sturdy dagger handled the endless small cutting jobs that come with living outdoors.
That doesn’t mean every soldier used his expensive military dagger as a can opener; a chipped blade still had to be repaired.
Mostly, the pugio was the sort of thing you were glad to have on your belt — even on days when you never needed to draw it.