This post's caught some imaginations and stirred up some memories: between 1989 and 1991 my Stumpy was built as a tourer for Europe, Thailand and India. Here's my recollections, in order of importance:
Steel frame of the best quality.
Forget about weight; focus on quality. The longjohns and hands of bananas & bottles of wine and stoves will make the finer points of weight weeniedom superflous.
Contact points:
Saddle: Kaiser is right. Brooks. Break in a B17 or better, buy a sprung one. Suspension seat posts aren't in it. Rear suspension is too cmplex; front suspension won't work properly and will leave you stranded in Botwsana, or Guam, or Streatham (many people can weld; small seals can be tricky to recreate).
Bars: HBars or high positioned drops or bendy bars that you like: Mary's; Nitto etc.
Shifters: Old school: thumbies or bar enders: Suntour ratchet or XT.
Grips: you know what you like best.
Pedals: know how to strip and grease them. Have the right tool. Dont try and rebuild an old campag road pedal with uncaged bearings on a sandy beach.

Power grips tha you can get big boots into.
Wear Points:
Tyres: surprisingly trouble free, but loads to choose from now. I used Tioga Farmer John's Knephews or something: they were cheap and heavy back then. No punctures; continuous road whine; interesting off road when unloaded.
Wheels: 36 hole bomb proof [Mavic M6s?]; DX or XT hubs. A few Spare spokes.
Racks: I only had single braze ons but managed front and rear racks, front low riders, camera bag on the bars. Spend money on good panniers.
Bottle cages: a decent touring bottle cage should hold a standard 75cl bottle of wine.
Gears: Lots: yourbike will be obese. I naively took 28:28 as lowest which was woefully inadequate. Rohloff sound fab but are they fixable?
Bungees & straps. Road test lots of bungees and take your favourites: they become more important than a lot of obvious things.
Brakes: don't know about disks they may be great. My XT canti/ubrake were trouble free over many miles (but watch for any odd tools you need to adjust em: 2mm allen key in a haystack?).
Tools: I was unprepared and lucky. If you really were going around the world then a minimum tool kit would make a thread in itself: decent pliers; multi wrench; odd tools like cone spanners & make-specific pullers etc,
Finally, a friend who was much more intrepid than I cycled from India to Turkey on a Claud Butler :shock: He said his best kit was a tennis racket to deflect dogs and the stones that urchins chuck at you.
