Wynand, as far as left over bait is concerned, put it in the black refuse bag that you brought with you. In my opinion the only thing ANY fisherman should leave behind is his footprints.
As faras casting over other other's lines etc. is concerned, I would not be fishing there.
I like to enjoy my fishing, in my "Own Space". Which is why flyfishing is so great, the f/f needs and is given space, so you are basically fishing in solitude, although you may be able to see the others on the river.
Fishing etiquette in it's simplest form is respect your fellow fisherman and his area of fishing.