Get a can of liquid air to blow away dust, fluids or other stuff (pro tip: get a compressor)
Get isopropyl alcohol for cleaning PCBs or other stuff.
Get brake cleaner to remove any grease (can also be used to clean PCBs).

Get chain-cleaner for your bike, which is basically a solvent and some oil (still needs greasing afterwards!).

Only use contact-spray if needed, better try isopropyl first!

Use vinegar or citric acid as a descaler to dissolve limescale - NO scrubbing!

Citric acid is used in so called “bath bombs”, reacting with baking soda.