All your set up is correct, @SeithCG!
And yes, all the joints in the skeleton that are shared between the two hierarchies need to have the same name, but any extra bone for the child can have its own name.
For example, if the backpack is attached to the spine_02, you would need to have this hierarchy: root, pelvis, spine_01, spine_02, then whatever you need, like backpack_root, backpack_dangling, etc.
Also, for any bodies you want to simulate using the Rigid Body node in the ABP, you need to set their Physics Type to Simulate in the Physics Asset.