i was thinking 1/2 pipe. with a blade made by myself, something very similar to a first blood knife or a AFSK. as i said the tang would be a tapered tang so id probly be from 7/16" to 3/16" . i was planning on putting a flint some fishing hooks and line, leather needles wrapped in thread, just the things that are hardest to make or find in the wilderness. im not sure what you meant by "Are you going to fill the pipe with something so your gear,does'nt wedge down between the tang and plastic?" but yeah every extra space will be filled with extra stuff and cotton balls for tinder and to keep it from rattling. i think the abs plastic would be pretty strong if its done right.
i had a knife with a thin walled plastice handle and the blade was just a quarter tang with threads and a nut holding in one end on the handle. the blade loosened many times before the handle broke, and it broke at a major stess point. so i think it would work.
i could use steel but that would be very heavy, and all the wieght would be in the handle so its no good for chopping. brass is the same with even more wieght and not as strong, also more expensive. i could use aluminum i think it would work well expensive but light and strong and is easy to machine.