When one of the spring anchor points on my front derailleur snapped off, I figured out how to stretch and tie off a cut-up inner tube to replace the spring. It worked, if anything, more smoothly than the original configuration. Rode the bike that way for a month or so until I sourced a replacement.

Episodes of the GCN Show and the GMBN Show on YouTube include a segment called "Hack or Bodge?," featuring examples of creative and/or wacky fixes.