Martin - I use your knot with my food bag, but only at night, in the rain, when I'm ankle deep in moose leavings.
Lofty's note interested me - the Sheet Bend is a super-helpful knot to know. For those who don't know, that's to join to ropes together of different diameters. Square knot does the same for two ends that are of the same diameter.
The use of a Figure Eight can be handy to prevent an end from slipping through a pulley for example, but if it is on the end of a piece of rope in general to prevent fraying, I find it a pain in the dupa because it interferes with untying knots. Still, depending on what you are using, you gotta do what you gotta do to prevent fraying. It did put me in mind of another rope skill - splicing, which you can do if you have a three-stranded rope (or more strands if you have a lot of dexterity).
Splicing is both fun and useful, it just takes more time than tying a knot, and I think most of the time we aren't using stranded rope (although we've all seen stranded rope when somebody loses a foodbag line....I'm hilarious). Stranded ropes tend to be thicker and heavier than what we would typically want to give packing space to or add portage weight for, but hey it is worth a mention, because splicing really is fun. At least I think so...
End splice (or back splice), is a way to finish the end of your rope to it will never fray.
Long splice joins two ropes together and retains more of the rope's strength than if you used a knot.
Eye splice forms a loop at the end of the rope, which is super-handy. I tend to tie loops in the ends ropes because it is faster and/or I don't have stranded rope, but the knot frequently gets in the way. An eye splice is a really clean way to accomplish the same thing.
There are lots and lots of splices, but I think you'd find the above three the most common and most useful.
So, to me, splicing would be a fun skill to learn, a fun in-camp skill to learn as well, and could be a fun in-camp skill to teach someone else. There has never been a person who made a splice who didn't want to show it off to somebody after they did it. The chief downside is you do a splice, then you wish you had more rope to splice and even if you do have more rope to splice you can't justify the utility of doing it just for the sake of doing it.