Is Premium or Mid-Grade Fuel Worth the Extra Money?
Premium gas doesn't provide any more power or contain better additives than regular gas, and it contains the same amount of ethanol as other grades. It just resists detonation (knock) better than lower-octane gas—nothing more, nothing less.
Some brands place slightly more detergent additive in their premium than in their other grades, but all grades meet the minimum required by the EPA. Bottom line? The carmaker knows best, so use the octane-rated fuel that's called for in your owner's manual. If your engine requires or 'recommends' 89- or 93-octane fuel, that's what you should use to get peak performance and fuel efficiency. But there is an exception to the rule.
If you have an older car that's designed for 87-octane gas and it knocks when you punch the pedal, try filling it with 89-octane fuel to see if the knock goes away. If so, keep using 89-octane to regain some power and save your engine.
How Long Can Gas be Stored?
If you store gas for your small engines in a tightly sealed container (allow some room for expansion at the top of the can), it'll last for a season. However, if your gas container doesn't seal tightly or you leave the spout off, airborne moisture and condensation can cause ethanol separation, oxidation and gum formation. Ethanol corrodes the carburetor and damages fuel line components, and gum, well, just gums up the works.
Adding fuel stabilizer to fresh gas reduces the risk of separation, oxidation and gum formation, but it can't compensate for sloppy handling. Investing in a better-sealing gas container costs a lot less than a carburetor rebuild.