Other than a seam ripper?? LOL. I think we're all way too familiar with that particular tool!
Other than the basics (mat, cutter & rulers that you have); pins which I'm assuming you have...a nice pair of both large and small scissors; hot iron - I can't really think of too many other 'necessities'. Needle & thread. Fabric. Batting. I'm pretty much a 'minimalist' when it comes to quilting.
I do suggest all of your rulers are of the same brand. Measurements do vary. I do have a small, spiral bound reference book that I believe is called 'The Quilters Reference Guide' or something close to that which I would highly recommend. Lots of good info in there and not too pricey. Fits nicely into the drawer of a sewing table (about 5 x 7).
Have as much do double duty for you as you can.