I have a stash of all consumeable parts- tires, tubes, chains, cables, bar tape, headsets, cassettes, chainrings, spokes. So I don't have to make it to the LBS today in order to fix the bike tonight so I can ride again tomorrow. I also have a rain/backup bike but in the winter I don't want to ride the good bike in the rain.

My backup bike, wheels, etc are old race bikes or parts from them.