I have purchased charm packs but sometime when I have made a quilt and have a little fabric left over, I will cut 5" squares and put them in a bag. That way I am not spending any more money. The 5" sqs I cut are like a gift. As a suggestion, if you are going to do this, you should cut 2 of each as some of the patterns require 2 of each piece of fabric.
We had a charm pack challenge at our quilt guild. If you wanted to join, you cut 50 sqs (2 of each fabric); put them in a bag and later when everyone that wanted to do this gathered and the packs of charms were exchanged and we made quilts. We showed them later at a meeting during our show/tell segment.
Have fun!