I've never made a backpack at all, I just toss everything into an enderpouch to be sent to sorting.I've never explored more than a kilometer away from spawn. I have some upgraded MPS legs now though, so I might make a lappack and bugger off for a while.
I never visit a cave twice. I try to grab everything there is in one go, especially things like iron. Yet I've also never made a miners backpack, so I'm using canvas bags way too much.
I've never really liked buildcraft, but it's the basis of my power plants. Yay for powerconverters!
I've never used Twilight Forest, my PC sucks and it lags me something terrible. (Which sucks because I really want to steal a lich tower for my base.)