Here are some ultralight keychain tools. If you put them all on a keychain they will weigh a total of only 45.5 grams or 1.6 ounces!
Nitecore Tiki Keychain Flashlight – 12 grams

Nitecore Tiki GITD Keychain Flashlight – shines at 300 lumens max – 12 grams.
Victorinox Swiss Army Classic Pocket Knife (Alox Version) – 17 grams

Victorinox Swiss Army Classic Pocket Knife (Silver Alox) – the alox version of this multi-tool is bit lighter than the regular version – 17 grams.
World’s Smallest Titanium Toothpick – 0.56 grams

World’s Smallest Titanium Toothpick — a portable toothpick made out of titanium — weighs only 0.56 grams.
Quick Release Titanium Keychain Clip – 7 grams

Quick Release Titanium Keychain Clip — ultralight titanium clip for a keychain – weighs only 7 grams.
Nite Ize Ink Pen – 9 grams

Nite Ize Inka Pen — writes underwater — writes in temperature from -30 degrees to +300 degrees — ultralight — made in USA — 9 grams.