You have the specific designed touring bikes that others have mentioned. I bought a Trek 510 this fall for the specific task of light duty touring - 2-5 days. The cost was a whole lot more reasonable than the 520's that pop up on Craigslist. Check out the mtb thread here - there's a lot of options there too if you can find one to fit. Those bikes can be had very cheap in a lot of cases. A friend of mine's college age son did a cross country trip on an old 80's road bike with 27" wheels a couple of years back and averaged 70-80 miles a day on it with hardly any problems.

Sounds like you're at the beginning stages of touring like I am. I've gone the mtb route and the Trek 510 because they fit in my budget - combined price for the two bikes was less than $60. That doesn't mean I won't keep looking for a nice touring bike like a Raleigh, Miyata, Bianchi Volpe, etc. or even something newer when it fits in the budget (i.e. the kids are out of the house).