bike Mechanics 101

We were going to go and do Sunset loop in Redlands(on of the stages from The Races there), but the weather forecast was calling for Santa Ana winds. I was going to be charge of the longest option(70 miles), but no showed except for a Tandem couple(Tom and Mary Lou) who was going to do a shorter option. I asked I could hitch a ride with them back. The winds weren't bad in the Morning, but were supposed to pick up, and lot of the riding was through some very gang-infested neighborhoods(I Think they would still be sleeping in the morning), just As I was getting ready to take off, I heard some one call my name. Another rider from the club(Fred Roth) had showed up. We called the tandem couple and told that we would be going west instead of east(they told the wind was "very bad").
Things went fine until we got to the midpoint of the Ride (Bonelli Park in San Dimas), Fred had pulled ahead on a hill. I was descending and saw him standing in the middle of the road with his bike . The Rear Derailleur had broken . We tried to make an emergency Single Speed, since we were about two miles from a shop, but had no luck. Fred eventually called his wife to rescue him and I went on my way. I discovered that chain breaker of my minitool was missing a piece, so I went and got a replacement. Had a flat, Stopped by REI and got a rack trunk, and went home (not wishing to press my luck) wound up with 53 miles