Some owners have complained that if you load the 300 up then it is uncomfortable to carry around. All I say to that is - if that's what you find then don't load it up with heavy equipment. I've had mine loaded up sometimes, and yes it may be a bit on the heavy side. But then you move it about, switch shoulders, take a rest once in a while, and generally stop being a pussy and get on with it. If you don't fill it with camera equipment then you can use the space to carry maps, rain jacket, food etc.
As for taking it overseas, I cannot get all that I want to take in the 300. I take my big Computrekker AW which holds my 17in laptop and all the stuff that I could not get on without should my main bag go astray. It just fits in the airline cabin bag size measuring frame. I put the 300 (or sometimes the 200) in my suitcase . I fill the 300 with socks, underwear, whatever, until it is full. That way it takes little of the suitcase space. At my destination I then take out for the day just what I want to carry around.
Check the San Francisco weather and be prepared. It may not be as warm as you would be hoping for. If you are planning on going to Alcatraz, then make your online booking NOW. It's almost guaranteed that if you leave it until you get there, you won't get a ticket. They are usually booked days ahead. Here's one place to book from
http://www.reserve123.com/index.cfm?go=products.tours&market_ID=1&Submit=GO
Take one of the city tours. The antique car (bus really, and not antique) and duck tours are quite good. the Duck (DUKW) drives in to the bay.
If you can stretch to it, try a 30 min flight in a Beaver seaplane over the city for $140. Find the tourist office on Pier 39 to book, or try the link above. On Saturdays they don't fly over the city, just the bay, so pick another day. If you have to, leave the kids behind. Tell them they'll be sick or something. Have a nice time.