Freewheel cone backed off, bearings lost, pawls didn't catch anymore -- found a long stick and "poled" my way back 10 miles or so.
Six or more flats one day on one wheel of my son's bike. Finally figured out that rimstrip was weak and letting the tube chafe on the drilling in the rim for one spoke. Folded up paper got us through.
Intermittent skip on indexed shifter; switched to friction and carried on. Found out that (for Shimano at least) it is important to have the "floating" pulley up top.
Jockey wheel fell off about a mile (downhill) from home. Walked the bike back, found jockey, washers, and eventually the bolt. Used loctite when I reassembled.