What was a possibles bag?

Answer 1

It was a bag in which you carried the various things you might possibly need.

Usually they were homemade, not because you couldn't buy one, but because folks liked to customize them to their own liking. You might also have more than one.

In a very real sense they were like an 18th/19th century briefcase.

Inside you would likely find stuff along these lines:

• Some means to make fire.
• Some musket balls and patch for your rifle, plus a few spare parts. Flints for instance, in the early days. Caps by the end of the Fur Trade era.
• Multiple knives, one or more of which was often carried in a scabbard on the bag's strap; as well as some assorted small tools the owner found useful. Sort of like a boy scout knife, but in multiple parts instead of one tool.
• A powder tin and possibly a measuring device. The owner might still carry a powder horn, especially if he was the sort who liked to use coarse grain powder behind his ball, but fine grained powder in his pan.
• Cord/twine, something of that sort. Possibly sinew.
• Cloth, from which to make ball patches.
• A sewing kit of some sort if he was going to be away from home for a while and thought he might need to patch something.

You get the idea...

There was no one style, the leathers could be from multiple different animal species, even in the same bag; and the contents were whatever the owner thought he might possibly need. Hence the name.