While 2.5" squares are little easier to come by (jelly roll strips and binding strips!) 3.5" squares are my favorite scrap size. This is a list of project ideas for using those 3.5" squares — hopefully these will inspire you to dig into your scrap bin!
(You need a mix of 3.5" and 4" squares)
(light valued squares only)
Of all of the various sizes of scraps that I have in my stash, the 3.5" squares always get used up the fastest so I try to cut more of them every time I cut leftover fabric.