So this morning when I bumped onto the sidewalk at the BART station and I was walking to the gate, my bike started acting like it didn't want to roll.
As I walked, I checked the brakes and the shifters, and everything seemed all right on that end. Finally I just carried it until I got to my chosen door location, and looked it over.
Somehow, my rear tire spear (axle) had come out of it's mounting on one side, so the tire was rubbing against the frame.
And that's why you always carry tools when you bike. The train was due in a couple minutes so I shucked off my helmet, vest, and gloves, and reached into my pack for my allen wrench. I almost immediately grabbed it and laid it in my helmet.
The trains are pretty empty at 6:15, so I got my spot with a seat, and quickly loosened the spear, re-positioned it, and tightened it up.
Everything's back to normal.
I'm not a Boy Scout, but I do my best to be prepared.