... how many should you buy? Assuming that you don't actually have a project in mind, at the time.
Can you do much with just one pack? Or should you buy two, if you love the collection? Or should you buy a jelly roll to go with it?
Or do you just buy a charm pack so that you can take it out from time to time and play with the squares? (Let's be honest... charm packs make GREAT toys for quilters!)