Under Construction You've seen the comment that you can solve 90% of your mechanical problems with duct tape and WD-40. Well it's not quite that easy and there is a plethora of products out there that you should not be without.
Protects hammers from corrosion.
Removes gunk from hacksaw blades.
Removes rust from saws.
Prevents rust on outdoor air conditioners.
Removes roofing tar from circular saw blades.

Duct Tape
Duct Tape comes in a variety of stickiness levels.
Top 10 Uses for Duct Tape : Science Channel

Acetone I primarily use it as a heavy-duty degreaser, it is useful in the preparation of metal prior to painting. It is also useful for high reliability soldering applications to remove rosin flux after soldering is complete; this helps to prevent the rusty bolt effect.
It is used for thinning polyester resin, cleaning tools used with it, and dissolving two-part epoxies and superglue before they harden.
Acetone can also be used in combination with automatic transmission fluid to create an effective penetrating oil. See:
Top 10 Things You Did or Didn’t Know About Acetone | I Can Has Science?
10 Unusual Uses for Nail Polish Remover (Acetone)

See glue guide here

See caulk guide here

Wood filler:
Plastic Wood
Elmers Carpenters Wood Filler

Rust Removal: Penetrating Catalyst Lubricant.
Loosens rusted nuts, bolts or pipe threads.
Also a water repellant to help protect against rust.
Rust Reformer and similar products A chemical like Rust Reformer should be used See:
How To Remove Rust from Metal FamilyHandyman
5 Tried and True Methods For Removing Rust From Metal Objects | ApartmentTherapy

See Removing Rusted Bolts

Loctite Product Advisor. Expert guidance to find the best adhesive, glue and sealing solutions. | Loctite Adhesives
  Loctite Threat Locker blue (regular) red (requires heat to remove)

RTV Silicone (room temperature vulcanization silicone):
RTV silicone - Wikipedia
RTV silicones are used for their ability to withstand mechanical and thermal stress.
Applications include aviation, consumer electronics, microelectronics engine electronics potting, and engine gasketing.

Cooling system thermostat selant.
Get it to stick in place with:
RTV (above)
or Permatex® Form-A-Gasket® No. 2 Sealant
or Permatex® the Right Stuff® 1 Minute Gasket™ GREY

See also:
Frugal DIY'ers, what's in your tool box? Which products do you keep around that you get a lot of use out of? : Frugal

last updated 7 Sep 2013