My two cents.
Most people should be aware that modern fuel 90 RON and above has quite a short shelf life, depending on who you talk to, around 3 weeks from pumping it out of the bowser.
My personal findings are that if its left in the fuel tank for a few months it goes off and resembles (cornflakes - a type of breakfast cereal). I had this happen to my Triumph Sprint when I bought it second hand from a dealer and it blocked up 2 out of the 3 injectors and was a royal pain in the arse.
I add an injector cleaner every few months and it prevents any blockages from occurring. Any good dealer should be informing you of this and keep minimal fuel in your tank if sitting for a long time. As for oils I have done oil studies for my work (gas turbines) and recommend not adding anything to your oil. All oils have additives already in them and if you live in an environment with low ambient temps ; then you should maintain the temperature of the oil in the crankcase to the minimum that the oil company recommends. Fairly common sense stuff