Learned my lesson after having to assist an MTB'er who had a compound fracture just above the ankle. Luckily I had a tampon that he used to stuff in the wound (I almost barfed right there), but I did not have any gauze bandage. Now I do.

Johnson & Johnson makes a mini 'kit' in a small plastic box with band-aids and wipes and such. I added gauze, aspirins (for heart attacks and strokes), two tampons, small vial of iodine and two large 2"x3" band-aids. Too much to fit in the little box, so put the box and the extras in a zip-lock and put it in an under-seat bag. Made one for each MTB and the commuter. The ziplock can also be cut open and used to keep dirt out of a bad wound like an open fracture.

On the road bike, I just don't have much room as I don't have a back pack to put the phone and repair stuff in. So I made a small kit. 3 alcohol wipes, 3 regular band-aids, 2 large band-aids, small vial of iodine and a few aspirins. I'm thinking If I need more, I am on the street and can get to a mini mart for more. Worse than that, I can call for help. It's when I am on the MTB that I need to be more self sufficient.