If you've got a hard set tune which really doesn't allow for any leeway with the ron of your fuel, then wouldn't be loading up the engine if its been off the road for a few months. But driving it down to the servo to get some fresh fuel into it will be fine.
Don't be letting it sit with a full tank of petrol for months and months though, since if a track day comes along and you've got a full tank of old fuel, you're going to gave a bad time unless your drain it out.
Also, I wouldn't be trusting Stale Fuel + Octane booster... Really not the same thing as fresh fuel