One thing I will do is wait till all the petrol is gone and fill it with super-unleaded. I read that normal unleaded (95 RON) goes off after a few months (yeah I know, but google it!) so super is better for the engine if used very sparingly.
95 RON was the regular unleaded prior to the introduction E10 (95 Octane) and is now classified as premium unleaded. Depending where you fill up super unleaded will be between 97-99 RON.