The local community airport has 100/110LL av-gas. It's pure gasoline with 0% ethanol or mtbe. It runs in $6.00/gal range (here now) so 5 gallons costs like an extra $10. Bring your own can. If they ask for a tail number (N-number) you can make up any three digits or tell them it's for an ultralight (they have no N-number). Or you can do what I do, glance at your RR with a stupid grin. Take your rocket fuel home, add it to a half tank of 93, crank the timing ahead about 5-10 degrees and have fun. Disclaimer - destroys catalytic converters and O2 sensors and legal for off-road use only.