I know the odds against my actually using a signal mirror are terrifically small; but its so tiny, cheap and if I ever did need it - useful. What tiny pieces of gear do you include?

UCO weatherproof matches

Fenix pocket flashlight

Swiss Army Knife Ranger

ResQbrite Signal Panel

Grill Starters

550 Cord

Contractor Garbage Bags

Or

Emergency Blanket

Or

Orange Bag

Aqua Pouch Purification Kit

None of them are large by themselves, together they can begin to take up some room. This is not an complete list.

very small LED flashlight

On keyring, everywhere!

house, car keys (natch!)
AAA flashlight
PS4multitool
tiny prybar
tiny lighter
cash (in capsule)

out in nature...
signal mirror
Ritter RSK Mk 5
at least one more multitool
matches, lighter, tinder (plus alcohol based sanitizer)
space blanket
AA headlamp w/ spare AA & AAA batteries in capsules
700 cc cup nested on canteen (at least one)
light jacket w/hood (Patagonia Houdini)
SOL Bivouac d'Urgence
whistle
base plate compass -usually there is a topo map as well
duct tape
FAK
food of some sort
hiking staff, various types

overnight add sleeping bag, tarp or tent, stove and fuel, pad and probably more clothing, depending on situation; all kinds of other gear depending upon circumstances

Depends on for what, but a few tiny but handy items:

- Leatherman PS4 multitool
- Petzl E+Lite headlight
- Superglue
- mini Bic lighter
- BRS stove

In the UK we have a shop that specialise in this sort of kit. I suspect you have similar in the US too.

http://www.edcgear.co.uk

My tiny fauxton light gets an almost daily workout. Its a keychain tool