Items required in a World travelling bike?
On a very long tour such as this, the cyclist will want to be as self-sufficient as possible. Bike components and accessories are often a trade-off between weight and cost, but touring brings durability and ease of repair to the forefront. 

This kind of riding is often called loaded touring, and has the strong implication that the cyclist is carrying everything needed such as food, camping equipment, tools, spare parts, maps, and sometimes more. There are other styles of touring such as supported touring, but I'm guessing the cyclist whose bike you saw wasn't doing this. Features of a bike suitable for extended loaded touring include: 


A comfortable saddle may well be the most important component of a diamond-frame touring bike. The cyclist will be spending many long days, weeks, months, or even years sitting on that saddle. The Brooks B-17 is an extremely popular saddle, and is common on touring bikes. Brooks has made leather saddles in England for many years. Leather saddles are comfortable because they conform to the wearer's butt over time, and may not be comfortable until they have several hundred miles on them. If you see a bike with an old, ratty-looking leather saddle, there's a good chance you're looking at a well-loved and well-used bike. 
Touring bikes need to be durable. This is a reason that steel frames are favored. Steel is flexible, strong, and can be fixed by welding. Steel frames are sturdy enough for racks to be installed on them. Other frame materials, such as aluminum and carbon fiber, are lighter than steel but aren't as strong. There are touring bikes made from aluminum, some of them good ones, but carbon fiber cannot at present take the weight of 30-60 pounds of panniers and camping equipment. Steel is also inexpensive. Unfortunately, steel is heavier than other frame materials. (This summary is a significant oversimplification.) 
Handlebars on a touring bike are a less-critical component, but bars that are a little wider than on a typical road bike are common. Since the posture of the rider on a touring bike will be oriented more towards comfort than on a road bike, riders often favor a more upright posture and handlebars are therefore set higher up. Handlebars may have room for accessories such as computers and lights. 
Wheels that are stronger are best, since a bike that is carrying a lot of weight will tend to break more spokes. A high spoke-count usually means a stronger wheel. 700c wheels are common on touring bikes, but 26" rims are more commonly found worldwide simply because of the availability of 26" tires and tubes worldwide. 
Tires will be selected for durability rather than speed. A tire that is faster but is prone to flats will slow the rider down more than a tire that is more durable. 
Navigation hardware can include a standard bike computer with an odometer paired with maps, a GPS with routing capabilities, or even both. 
Sturdy racks are important. Weaker, inexpensive racks will bend and break under a heavy load. Most racks used for touring are sold with a maximum weight capacity figure. Tubus makes an excellent selection of touring racks. 
Panniers will be selected based on durability. The question of whether a rack will have many small pockets or one large one (i.e., a simple sack with attachment hooks) is a matter of packing style and personal preference. Ortlieb and Arkel are two higher-end touring pannier manufacturers. 
Drivetrain components should be durable and easily fixed on the road. For this reason, internally geared hubs are seldom used, even though they are generally more trouble-free. A traditional derailer can be fixed at the side of the road in many cases. A gear ratio should be selected that allows for hill-climbing, even at the expense of sacrificing speed. Bar-end shifters are often favored, because they're simpler to fix than more complex shifters. 
Suspension is often not used on a touring bike, since they are less efficient at translating pedaling into forward motion. However, there are offroad touring bikes. Suspension also makes it difficult to attach racks, particularly rear suspension.  
Brakes are usually rim brakes, for similar reasons as drivetrain components: they can be fixed with few tools. However, disc brakes are starting to be more common on touring bikes. 


Common touring bikes include the Surly Long-Haul Trucker and the Trek 520. (The Novara Randonee is essentially a clone of these bikes.) Rivendell and Bike Friday also make well-regarded touring bikes; there are no doubt many other manufacturers of sturdy frames. Steel hardtail (non-suspension) mountain bike frames can be converted into touring bikes relatively easily. 

There's an old touring adage: You can tour on any bike. Carbon-fiber racing bikes can pull a trailer full of gear. The above outline of what's helpful on a touring bike is what I would consider a best-case scenario, but is by no means mandatory. 

I'll close this with a picture of one of my touring bikes.