I have two "go" bags.
I am a substitute teacher. Some days are jammed packed with children, some days I have 1 1/2 hours to wait. So...
One bag is rather large. In it are small scissors, thread, needles, ribbons, yarn, leather strips, small metal chains and charms,etc; anything I could use on my Stupendous Stitching items.
The second is small; containing a sketch book, pencil, sometimes a small book on hand stitching or something, sometimes scraps of material I'm working with at the time (and if I'm going to be with little ones that day, perhaps a book or two to read to them).