I did my first decent length trip this past summer with my '76 CB550. Most of the bike was gone over, with the help of these folks here on this forum.
After 1300 miles, I really only had a few electrical gremlins which I was able to sort out in the parking lot of a motel. As already stated, these bikes, if set up correctly, seem to be able to handle these trips just fine.
I packed pretty light, bringing only what I thought I would be comfortable changing on the side of the road (wire, plugs, cables, etc), the rest can be purchased from one of the 48,000 auto parts store you will encounter along the way.
The only things I would add to the great suggestions already: decent gloves (preferably with gel/padded palm area), a $20 gel seat cover from Walmart and cash/CC.
I really believe that touring on one of these bikes, and really any bike, is ultimately made comfortable by a mindset. Having done the thorough tuning and check ups, and knowing you can pay for a tow, motel, meal etc if you are broken down, frustrated or at wits end, makes the trip that much more enjoyable.
Can't wait to read the ride report!