I do personally run on Dunkin Donut's coffee. I have a nearby location that serves a very consistent "magic cup" of coffee. Perfect for most workdays when I need to switch into 'run' mode.
What does my Monza run on...? My Monza was tuned using Sunoco Ultra93. That mean's when I adjusted the idle mixture, and dialed in my distributor, I was running Ultra 93.
I can get away with 91 octane "Premium" (found at most all other retailers stations) However I have to listen for 'detonation' or 'pinging' as you might call it.
Any less and It'll definitely ping. My initial mindset for tuning the engine to this fuel is as follows.. Most sources say for maximum power tune the engine timing for the most timing it will accept before it ping's and looses power.. (dangerous detonation). And Ultra 93 allowed for the most timing I could dial into the motor. And as such it sure feels strong and crisp. Run's cool too. In fact a little too cool most of the time, so the timing I have dialed in isn't contributing to any type of run-hot condition, barring running the car at 4000 RPM for 30+ minutes in the mid-day sun, heat and humidity... but I don't find myself stunt-driving like that anymore anyways.
The 2nd reason for tuning for Ultra 93..was the need to use a fuel with greater knock resistance, as is the case with Higher Octane fuels. Why? My Monza still has the factory 305.
In Stock form, the 305 used dished pistons and a pretty basic and low; 8.4:1 compression ratio.
Even still it used tiny 57cc chambered heads, and was designed to run HOT for emissions purposes.
With tiny valves and propensity to build up carbon in the chamber detonation was a concern for early lean-running, emission-tuned 305's.
My Monza however, has been updated to heads from an '83/'84 305HO motor. Larger valves and a little better flow are the advantages of using these heads. The also have a slightly larger 60cc chamber, and are made to run with a flat top piston.. And lucky for me.. mine has been dis-assembled and bored .30 over and refitted with Flat-top's, with 4 valve relief's. Good again for compression.. @ 9.5:1 with a reg head gasket.
Good therefore, for performance, but these were still made for an emissions tuned hot running motor. So with detonation still in mind, I opted to tune to Sunoco Ultra 93.
Plus lucky for Sunoco they are the closest fuel retailer to my garage bay. Their sticker's also made a great cover for some recent blemishes that found their way onto my daily driver - Chevy Aveo.
I have read in recent years, about power tuning a normally aspirated engine for 87 octane and making excellent street power, but that was on an 8.4:1 350 engine.