I almost bought the Cortech bags, but I found some at a local dealer last year and hated the red cotton lining. Looked like it would pill up immediately once you stuff velcro cuff gloves in there a couple times.
I bought the Nelson Rigg CL-2014:
Amazon.com: Nelson Rigg Magnetic Mount Motorcycle Bag (Black,Medium),1 Pack: Automotive
Not sure how many liters it is, but it's medium sized I'd say and sits below the instruments. When expanded you get an extra 2.5" deep. It'll easily fit a bunch of 20oz waters + sandwichs. I've used it for shopping runs, and 1000 mile rides. More expensive than most, but has a lifetime warranty. The magnets are well positioned for the Scrambler tank, they all land on steel surfaces not the aluminum panels or gas cap.
With magnet bags you'll want to make sure the tank is clean because vibration will grind up the paint. The early Scramblers had super thin tank paint. Not sure if they still do, but mine has barely begun to wear in a few spots (above the gas cap mostly). Doesn't really bother me. I'll get to repaint sometime.
Related: those are the larger Kriega bags. 100% recommend that system.