Moto-Detail (from getgeared.com) small magnetic tankbag. Several magnets and a headstock strap to keep it in place. Hard rubber carrying handle. Volume is about 4 litres, you could fit a small bottle of water and some sandwiches in here. Used a couple of times and in top condition, not used it for ages. Now I either cram stuff in pockets or a full size tankbag.
Comes with a waterproof cover and some internal dividers.
Ideally suit some comms equipment but I never got round to it. £5?