To be clear, we're both talking about road bikes here.
Besides things like rack mount points, the differences between fitness/racing bikes and touring bikes are in the bike's geometry, like the vertical distance between the bars and the seat or the angle of the head tube.
Other differences include that touring bike frames tend to be stronger, and they have lower gears.
Also, it has a frame that can accommodate wider 700Cx35 or 38 tires, which gives you the low rolling resistance of road tires, with the traction and bump absorption of fat tires. Regular road wheels will transmit too much vibration and be fatiguing (assuming they don't just break from the weight), but most 26" wheels add a lot of resistance.
I rode my 1978(?) steel Univega Grand Tourismo touring bike from SF down the coast of CA through Baja Mexico, took a ferry to mainland, then rode down the coast of Mexico to Acapulco, then went back northward over the mountains to Mexico City when I was 19.
The original plan was to go all the way through South America, catch a freighter to South Africa, and ride up to Europe.
This plan was derailed when two of my 3 riding partners decided to get divorced after it was revealed that one of them had developed feelings for the 3rd one!!
This still left me with a 2 month, ~3000 mile bicycle tour - the last 3rd of which I did solo.
We did more camping than hotels. I carried tent, sleeping bag, therma-rest, camp stove and gas bottle, bike tools, spare tire, spare tubes, lots of extra water, shoes for off the bike (cleated clipless for riding) and of course clothes and junk; it all came to almost 70lbs of gear on my 30lb bike. The grand total was nearly as much as I weighed back then.
And you know what I learned?
Its actually really, really easy. You just do it.
The only real problem is being able to afford taking weeks or months or years off of work (in my case, I was designated as trip mechanic and translator, and was fully paid for).
The only problem I encountered was language (I failed in my translator duties.)
More specific tips though:
-if you use panniers (and I'm on that side of the debate, why have all the extra weight of a trailer if you can avoid it?), load the front at least as much, if not more than, the rear. It seems counter-intuitive, but a loaded touring bike handles better with the weight up front.
-make sure either bags are waterproof, or put everything inside garbage bags inside them.
-start your shower each day with your clothes on, then take them off in the shower and stamp them clean, and tie them to the rack the next day to air dry. That way you can just cycle the same two sets of clothing indefinitely
-have a big handlebar bag with lots of pockets and a map holder so you can grab stuff without having to stop. Touring is not like commuting or a pleasure ride; its more like being a trucker, you're just moving all day, so you want everything you might want accessible from the drivers seat - food, phone, glasses, jacket, map, mp3 player, whatever
-try to use bike and components that are common and universal. Hydraulic disk brakes might be powerful and work in bad conditions, but when something breaks the closest thing to a bike shop in town is WalMart, you're going to wish you had standard brakes.
-try to find ridiculously low gears. Possibly even approaching a 1:1 low gear. Riding at 5mph uphill into a headwind still beats walking up it at 3mph.
-give yourself at least a 20% margin of error when planning your route and miles covered each day.
Nothing sucks more than getting delayed and ending up riding on a cracked hub with no rear brake in a thunderstorm at 9pm, still 15 miles away from the nearest town or campgrounds, because you assumed you could ride 110 miles in one day just because you had been the past few days and you didn't count on one giant pothole that would crack the rear wheel. This matters less if you are staying near civilization at all times, but going around the US will probably put you through some pretty isolated stretches.
-most important of all: if you go with anyone else, you better be absolutely sure you can stand them 24/7; even when you are both tired and stinky and hungry and wet, and some unexpected problem comes up and you both have different ideas of how to handle it. If you go with more than one other person, also that they can stand each other in that circumstance.
