How about lithium carbonate? Used for decades to treat mood swings/bipolar disorders in the mental health field, and has loads of engineering/building applications eg glass manufacturing, cement additive etc.
I say, start with the basics. Ignoring all the different detailed applications, good old H2O is used in a huge variety of ways:
as
a solvent
a mechanical force transmitter (hydraulics)
(washing uses both the solvent and mechanical properties)
a non-reactive liquid carrier (water-based paints, etc.) and a non-reactive medium for sustaining chemical reactions
a liquid coolant
a solid coolant
a liquid heat conductor (e.g. boiling pasta)
a vapor heat conductor (e.g. steaming vegetables, steam radiators)
for turning heat into mechanical motion (steam generators)
a seal against vapors (plumbing trap)
[arguably as an electrical conductor, but it has to be doped with something to do that]
In some cases, as a solid building material (ice roads, snow berms, igloos), and in extremely limited cases as an insulator (snow shelters)
Baking soda–cleaner, whitener, polisher, abrasive, medicinal, deodorizing, absorbant. It does it all, and is completely non-toxic and environmentally friendly. AND very very cheap.
Okay, yes, I suppose that’s probably true, but I’m looking for common uses, particularly ones that are just so different as to raise eyebrows. Nitroglycerin is an excellent example.
Lye (sodium…hydroxide?): make soap with it, speed decomposition, clean your oven, and mercerize cotton (that is, make it shinier and more porous to dyes).
Why, how about Sal Ammoniac, a.k.a. ammonium chloride?
According to Wikipedia, it’s used as:
an electrolyte in dry-cell batteries
a fertilizer for rice
flux
a cleaner for soldering tips
a feed supplement for cattle
an ingredient in shampoo
part of the glue in plywood
an ingredient in nutritive media for yeast
an ingredient in cough medicine
a spice for liquorice-type candies
a flavoring for vodkas
Also a structural material, when combined with epoxy. (Though I admit I never understood that one - how can something be soft enough to write with, and hard enough to be a structural material?)