The other ruler that I use when trimming quilts is the 22.5" square ruler which is great for squaring up the corners of a quilt. I recommend the large rotary cutter if it's in your budget as you can cut more layers of fabric in one go. I only remembered this after I had cut several separate pieces of fabric for my scrap strips. Also buy the largest mat that you can afford. The blue mat is a3 in size but I might swap it for the a2 may that I keep under my sewing machine upstairs.
Here is my fourth scrappy trip around the world block.
And this is a picture of the four blocks to date.
What size ruler do you use the most and what one have you not used as much as you thought?