I just got and stuffed a banana bag from fairtex. It weighs 117 lbs now and is stuffed completley with rags.
I used rags because I've seen sellers of heavy bags BRAG about their bags being stuffed with "100% rags" (check out aries site to see what I mean)
I used old bedsheets and clothing from around the house, this was maybe 35 lbs worth. I purchased ~ 80 lbs of sheets from the bins @ goodwill for .67/pound. (I'm impatient) I just folded the sheets and cut them into strips, about 4-8" wide and cut the strips to about 18" long. I left them in the hunks that foldedd sheets end up ion when you cut them for the most part as I made a pile cause they are pre-packed that way somewhat. After the pile got big enough (about 4 sheets worth), I grab it and just stuff it in the bag, trying to keep the sheets lying flat relitive to the bottom of the bag.
To pack it, I'd put in 6-8" at a time stuff my legs in , grab the sides of the bag and ram it in with my legs. As it got fuller I could loop the straps against my forearms and really push. This made the upper parts of the bag slightly denser than the bottom, which is nice since it will settle anyway.
As I said, I got it to 117 lbs using only rags in one go. Thinner stuff like bedsheets are the best because the high thread count makes it heavy when it's packed. much denser in rolls than most denims, canases, and especially carpet and blanket. Some rugs can be dense, but I avoided using them. No sand was needed and I'm sure I can easily get my fairtex bag up to 125 lbs with a week or so of settling. (for clothing, dress shirts, skirts, t shirts and slacks are decent. Sweats, and sweaters are not desireable.)
The hardest part was cutting the cloth into chunks/strips, that took 12 hrs spread over 3 days
Hope it helps
Chaghatai