When our Cairn Terrier became more elderly I did have carry him while backpacking over portions of the day. He just didn’t want to stay home. I don’t think the top of the pack is a suitable place but some might make it work. I put him in a small Eagle Creek duffle with a piece of closed cell foam in the bottom that was curved on my body side to fit and two shoulder straps worn sort of backpack style in front, bag to my stomach. He loved it. I’d let him walk when he wanted but would put him in the bag when he needed that. We could communicate with looks and gestures so he could tell me.

In the end it depends on what you like and just how much you are willing to put up with. We enjoyed his company over the 17 years with him and depended on his hearing and olfactory skills that were far beyond our own.