[Nyororin]

As long as you have a return ticket and don`t plan to do anything like working (which you would require a different visa for) - Yes, that`s all you have to do.
Japan has a tourism exchange thing going with the US, so citizens of the two countries are granted a 90 tourist visa upon entry into the other. The return ticket isn`t for financial stability, just to make it clear that you plan on leaving and not overstaying your visa.

As for luggage not making it, well, that`s up to the airline. Some airlines and airports have better reputations than others. The Japan side is quite efficient - the US side, not so much so.