My favorite method is also the rectangle with two squares. When I trim, I keep the two scrap triangles together in a zip loc baggy (quart size) and then use them as leaders and enders making HST. Typically, from a FG unit that finishes at 2" x 4" (the size I seem to use more than any other) the scrap HST after squaring up I can get an unfinished 1 3/4" HST. Many times I further trim down to 1 1/2" size as I use that size a lot more. I then store the squared up HST in zip loc bags according to size. I am saving them up to make a tree of life scrap quilt but there are thousands of block patterns that use HST.