A couple weeks ago I flew standbye on UA SFO-ORD-ATL. Getting on the fully loaded 777 I was not allowed to carryon my small carryon. They had to check it. I got to ORD with my next flight boarding in about 45mins, and went to baggage claim, my bag never came. I showed the ticket for it, and the agent had no idea where it was. I got on my flight with nothing, and it was canceled because of engine problems, so I ran back down to the claim area, and went to cust service. Well the back somehow got on a flight going SFO-LAX-Somewhere like China. Because the flt # was misread. But in LAX Someone saw the ORD destination on the bag, and got it on a ORD Flight. Amazingly the bag was was waiting for me at baggage claim from LAX. I got it, and got on the plane that they got for us, and took a shortcut to ATL, and almost made it there as scheduled.