A few more:
Disposable Nitrile Rubber Gloves:
These things are great. Very inexpensive, tear resistant, chemical resistant, and disposable. You can even clean dirt and grease off of them with a solvent as you work to prevent spreading contaminants where they do not belong.
Unlike bulky gloves, these are thin, so they maintain the 'feel' and dexterity of your fingers, and the rubber improves your grip.
Fold the cuffs over to prevent oil from running down your arm! They can get uncomfortably sweaty on warm days.
Popsicle Sticks:
The perfect tool for neatly applying greases or adhesives. They will not scratch precision part (bearings and such), and they can tool a perfect bead of sealant. Great for mixing epoxies, and they will not melt when the epoxy gets hot. Can be split to size. A new one is always clean!
Disposable Wooden Spoons:
Similar to popsicle sticks, but they have a fatter paddle shape. Better for some applications.
Used Toothbrushes:
Great for scrubbing small parts or nooks and crannies.
Stanley Multisaw:
Holds a hacksaw blade or a sawsall blade. Unbelievably useful.
Permatex Aviation Form-a-Gasket:
This relatively thin and very sticky material is better than thick rubbery sealants (like RTV) for many purposes.
Forms a great gasket on closely matched parts. Good for fortifying a gasket, particularly the paper ones. Also good for holding a gasket in place during assembly. Curing can be accelerated with heat as needed. Even rated for fuel tank use.
Freezer:
Any pressed part will go in easier after some time in the freezer. Contraction is a marvelous thing. Try this with bearing races or balljoints, and you will be amazed.
Coathanger:
The perfect tool for suspending a brake caliper, but can temporarily hold heavier things too. Try using one to prevent your exhaust from falling on your head when you detach it, for example.