I actually have 2 bags that I use for quilting on the go.
One is for yo-yo's: It is a silver cosmetic bag with about 100 cutouts of the yo-yo circles, snips, yo-yo maker, package of needles, thread heaven, thimble pads, pliers, seam ripper, thread, plastic bag for the finished yo-yo's; rubber gripper, and a notebook and pen.
The second is for applique or regular sewing/quilting: I have a seperate two sided cosmetic bag, which contains duplicates of the above plus pins, a thumb pin cushion, ruler, sewing machine needles, glue stick, marking pen, tape measure, calculator and a rotary cutter.
Depending on where I am going and how long I am gone, I just grab the bag and go.
With the second one, I also grab the project I am working on, a small cutting mat/ironing pad and travel iron, along with my Featherweight. This is usually for an overnight trip or a vacation.
I can be ready in a couple of minutes!