In addition to a whole shelf full of commercial contact cleaners, lubes, parts cleaners, adhesives, etc., I keep a handful of "raw chemicals" around:
IPA--general cleaning and solder flux removal.
Acetone--degreasing, paint removal, thinning adhesives.
Methanol--cleaning optics.
Xylene--removing stickers and adhesive residue.
Toluene--same as above, when xylene won't work.
Dichloromethane--solvent welding plastics, softening epoxy potting compounds.
Methyl salicylate--restoring/cleaning rubber drive rollers, etc.