I think your son will be too big for the United bassinets. Being from S.F. myself, I fly them a lot with my kids. On U.S. companies, I always bring a car seat so I actually haven't used them.

Taking a car seat is actually the only way to fly safely with a baby. If he still fits in the infant bucket-style seat, then you can use a stroller frame and that would be your stroller for the trip. Ask at check-in if they can "block" and empty seat next to you so that you can use the car seat. This is not only safer but much, much more comfortable for all of you (and those seated around you).

I had one of these. It's pricey but was very useful for international travel, both on the flights and public transport;

http://www.lillygold.com/

Just thought I'd mention it. I can't really recommend it unless you plan to do a lot of travel and/or have more children. It's also a solution for cabs...

I've also been to Japan many, many times. I love it but I have yet to go with my little ones (they're keen though! They inherited mommy's travel lust). I do have experience taking transport in several major cities (Paris several times, Barcelona, London, Rome) and whatever stroller you take, make sure it folds quickly. I loved the MacLauren for that. I could fold it with one hand. Try to "exchange" a stroller with a friend if you can, or get one second hand if you don't want to dish out for a new one. My Peg Perego didn't fold down as nicely for the Métro but they may have improved the design since my oldest was little.

I really recommend a good baby carrier. I had a Bjorn for my son but it was unusable by the time he was 6 months old. A good carrier should go to at least age 2. A wrap, sling or pouch is ideal. Some people like carriers like Mei Tai's, Beccos or Ergos. Here are a couple of sites to check out with multiple companys' products;

http://peppermint.com
http://kangarookorner.com

Not only do they make travel easier but your whole life. I could get so much done with my baby tucked away comfortably and not hanging by its' crotch with all sorts of fiddly straps and buttons like the Bjorns have.

I take a backpack for a diaper bag (when mine were in diapers, which was 7 staight years in our case!) and I put my valuables in a small bag in front, around my neck so I could keep an eye on it.

One of my children had formula and I used the kind of bottles with disposable liners. I premeasured the powder and rolled the bags up, only having to add water when I was on the flight or anytime I was out in public. Since warming a bottle has no health advantage, be sure he takes his room temperature. They warm them on the flight but there isn't anyone to help in the check-in lines, security, Tokyo subway, etc. Save yourselves that pesky task while traveling.

http://www.tsa.gov/travelers/airtrav...n/formula.shtm

Japan is very safe and you have little chance of being pick-pocketed. It's also super clean and even in a thick crowd, people move very efficiently, almost amazingly so. You can get across a crowded intersection without anyone even touching you, let alone bumping into you and the baby.

The Japanese are also baby-crazy, especially an exotic white child. If he's blond and blue eyed, the attention he gets might be your biggest problem (and another reason the carrier is a good idea). They are simply curious and admiring but it might scare your little one, so be warned. Try to ward off any incidents (i.e. picking him up if someone is getting too close).

Here are my totally non-commercial flying tips, based on both flying with my three children internationally and my 13 years of working as a Flight Attendant, almost all long haul for two major companies;

http://flyingwithchildren.blogspot.com

Have a great time!