If I'm shopping with no pattern in mind and I see a fabric I like I usually get 1yd, especially if I think I can use in a scrappy quilt, if I really, really love the fabric I get 3yds (I attach a note with place, name and date), if it's a fabric that might look good as backing I usually get 5 yds (again, can cut up for futue scrappy quilt). I tend to not buy FQ b/c of the price.
Just my shopping ideas; but shopping for patterns may be the way to go until you build up your stash for that scrappy in the future :) :)