Probably mentioned already but for a while I just used dry wall screws I had in the garage. The flat round head worked fine. I now have like 3-4 pipe tools plus a tamper/spoon combo that came with a pipe order. At one time, I had misplaced every pipe tool I had, then they all pop up out of nowhere. I never lose them, only misplace them.
actually, i do not own a real tamper. i use in this order
a case bone pen knife which is my A. P. pipe tool
peices of random wood from my wood kindleling box and i'm sad when my wife burns one in the fire place
A friction fuse ignitor. Note: the ignitor, NOT the blasting cap!
A live 5.56 round. C'mon, be realistic, it takes more heat and more time to "cook off" a round than a half second tamp. Especially at 40 below. round was probably frozen anyway.
Just about anything really that will get the job done if I don't have a real pipe tamper handy. My favorite tamper is a deer antler tamper with a .45 shell casing end that I purchased from Don Warren. That tamper just seems to had a bit to my enjoyment.