Been using scrap Avgas in my cars for 30+ years. It is virtually identical chemically to Sunoco 102 octane gas that was available in the 1970’s. Best gas that you can get! Especially when it is free…
Aviation gas 100 LL contains about 28 grams of TEL per gallon minimum. The octane is achieved through the use of that amount of TEL, and Iso Octane which is simply refined petroleum. In other words there is no ethanol and no additives to degrade and turn sour in your tank. As such it has excellent storage properties, and can be just fine after 12 months in the can or your car’s tank. Airplanes have to operate from the Dead Sea airport in Israel up to perhaps 25000 feet for some high performance turbocharged aircraft, so the vapor properties are also excellent.