For many a bike is a stripped down collection of steel, alloy and carbon fibre with as little weight as possible. I always consider these beasts to be the cycling equivalent of formula one cars, designed with speed as the number one priority, and with little thought for any practical use. For the tourist priorities are a little different, and I suppose a lightweight tourer would be more akin to an Aston Martin, or in some cases a Transit Van! -Yes a touring bike needs to carry loads, and so is a very different design to the racing mount.
How much your bike will need to carry depends very much on the kind of touring you do. If it's a weekend dash between hotels you can get away with a couple of changes of clothes and a wash kit in a small bag, but for serious touring, especially cyclecamping, loads will quickly rise to 30, 40 or even 50 pounds. Obviously the weight you carry will be down to your parsimony and how much you spend on your camping kit. Camping, like cycling is one of the few areas where less (weight) costs more. If you are starting to get to the upper range of weight, perhaps this is a very long tour, or in cold weather, then a simple pair of panniers will not suffice. Weight must be spread over the bike. Here there is a split between the traditions of the continent and the English speaking world.
On the Continent tourists swear by carrying the bulk of the weight on large front panniers, with the rear rack carrying the tent and little else. This has considerably advantages, most notably that it takes a great load off the already overstressed rear wheel. I also read a very well argued article by a well known cycling writer explaining how the bike was much more stable as the weight was nearer the steering axis. This of course was complete bollocks as I found when, after arriving at a campsite with my son in a baby seat, I went shopping with only one large front pannier leaving the other back at the tent. The baby seat stopped me using rear panniers incidentally. After buying my goodies, two bottles of wine etc, totalling I suppose about 10 lbs, I attempted to ride off. It was in fact impossible, the bike pulling violently one way then the other. I had to push the bike... I've done this with one rear pannier many times and not even noticed the uneven load. The moral being that if you choose the continental option then even loading is essential. The effect on the steering of the bike is also rather unpleasant even if the panniers are even, pothole dodging being very difficult as with any sudden move. There is also the consideration of fork collapse, they are not designed for heavy weights and unlike the rear of a bike there is no triangulation to support them.
Personally I, when babyless, use the classic front/rear pannier mix popularised by Blackburn amongst others. Here the rear panniers carry about 2/3 the weight, and the front are mounted low down on "low rider" racks which help keep the centre of gravity low. The tent then goes over the rear rack. This produces a well balanced and responsive bike, providing the frame is stiff enough not to twist back and forth under the weight and cause speed wobble. The rear wheel does take a hammering, and it essential that this is as strong as possible (see previous articles on hubs) and you need to be able to repair broken spokes in extremis.
As for the racks you use, cheap alloy one's are a disaster. I've a workshop full of the wreakage. You need to buy the best alloy racks, Blackburn, ESGE, use price as your guide, you get what you pay for. Perhaps better still are steel racks, not only are these less likely to break than even the best alloy racks, they can be easily repaired by any garage/blacksmith.
The only other alternative is the Yak BOB trailer or similar, where all the weight is carried off the bike. It's a very attractive option which you can read about in the review of the BOB in a previous issue.
Whatever you do, the secret is to let the bike carry the weight. Every year I see touring cyclists with huge backpacks, all I can say about this is that it is uncomfortable, hot and dangerous. People generally only tour like this once...