Another favorite in my trusty toolbox is my Campagnolo 'T' Wrench. Introduced around the sixties.
Well balanced, measuring just under 4 inches, palm size this little dynamo has a 8mm socket wrench and a 6mm allen wrench 'T' handle. Nifty to remove or install the rear derailleur, front derailleur, tighten derailleur/brake cable bolts & the handlebar stem.
This essential beauty always comes through in the pinch... I'm so glad to have it!