[sarasi]

You may not need a 14 day JR pass- unless you do a number of long trips on the shinkansen (not just Tokyo-Kyoto-Osaka-Tokyo), it may be cheaper to just buy single tickets. Have a look at train travel planning sites like hyperdia to make sure you really need a JR pass before spending all that money.

Power outlet convertor, i.e. adaptor plug? You may not need one. You don't say where you are from, but I'm assuming you are from the US since (sorry for the generalisation) on the internet it is usually Americans who don't say where they are from and assume everyone just knows!

As long as your plugs are two prong you won't need an adaptor. If you have anything with 3 prongs then you will need an adaptor.

Japan is one of the world's safer countries- yes, you can travel by yourself without worrying, just use your common sense while you are here. I first came to Japan by myself just after my 20th birthday.

I don't know about gifts- unless you are coming to work or will be doing a homestay, I can't imagine who you would give them to. You don't need to give anything to hotel staff etc.

Rather than a handkerchief, it's better to have a small towel for drying your hands in public restrooms where there is often nothing to dry your hands with. This is not compulsory though! People use tissues for blowing their noses here, and generally try to avoid blowing their noses in public if they can.