A multi-tool or a knife?
A multi-tool can be a very appropriate tool for backpacking. It combines the function of many of the tools you mentioned. You may carry the tools you mention above, though. (Note: I've NEVER needed a bottle opener...)
If you mean a knife, read on...
I do a lot of backpacking in the Eastern US, so I am going to assume that this is the equivalent of "wild camping" in Scotland. In fact, I've just returned from a five day trip to the Cohutta Mountains during which my knife was used for:
- preparing food (peeling fruit) and other general cooking tasks (opening packages). Yes, I keep my knife clean and usually boil it in my sterilizing/wash water daily.
- preparing fires. Where I camp, it is typically quite damp much of the year, so we make feather sticks or other tinder (by shaving wood) when necessary. My go-to fire starter is a ferrocium rod, and I use my knife as a striker.
- working with cord. I carry several types of cord (paracord, jute) for general camp tasks, including bear bagging, rigging a tarp, and clothes lines. Occasionally, a line or knot will become stuck or jammed and must be cut. Just two nights ago, my bear bag line became trapped in the tree and had to be cut. Not having a knife, I would have had to leave 50 feet behind, but instead I lost only about 8 feet. Lengths of cord are often cut when shorter lengths are needed (this is where I use jute). There are MANY uses for cord in the back country, and is one of my essential items on any trip.
- First aid, such as cutting moleskin or gauze pads to fit a wound.
I will agree that there is not much need for a large fixed blade knife during backpacking activities. However, I just completed an advanced bushcraft course two weeks ago and we used large knives (4 to 5 inch blades) extensively. Simply put, bushcraft is the art of creating what you need from what you have in the backcountry. If used correctly, these knives can be used for serious woodworking (shelter, furniture, etc) or firecraft (crating a bow drill, splitting wood) projects.
Even when I have my large fixed blade knife, I tend to carry my small folding knife to handle the fine/delicate tasks that a large knife cannot do easily (or safely).
On a typical backpacking (or wild camping) trip, I would consider a medium sized (2.5 to 3.5 inch) locking blade knife an indispensable item. In fact, a knife is listed as one of the "10 essential items" on both the classic and contemporary lists (see http://www.rei.com/learn/expert-advice/ten-essentials.html) for any backcountry trip.