One piece of clothing on our world trip that ended up being as valuable as anything else in our panniers was a down jacket. Sounds odd, but as has been pointed out, if you are going to travel extensively in one period, that time is going to include cold weather somewhere, even in the middle of summer.

Those down jackets were mighty useful on numerous parts of our travels, among them being a trip up Mont Blanc, in Scotland, in parts of France, and of course, in North America.

A down jacket can be packed down to a small, light size, but the trade-off is that you need to protect it from rain with another waterproof jacket over the top (we had one each anyway), and cycling in them can be a bit dicey because of the sweat absorption.

But if we were to travel like that again, the down jacket would be one item on the list.

Having said that, others' observations about taking less than you would on a short tour works to a certain extent.

Spectastic, seeing you have done some cycle-touring now, just what do you think you would need to take extra that you don't already have? The list you posted gave some options for what you already have, but appear to be upgrades with perhaps weight penalties. There are some things on your list that I wouldn't bother taking with me, but that's all down to personal preference.

To explain a few more things. The panniers on the fixed gear bike illustrated by Machka were actually smaller than the ones on the RTW trip. And the RTW panniers weren't packed to the gills until some way into the trip as we bought clothing (we love shopping at the French Decathlon stores) and odd things such as a beach paddle-and-ball set, and a frisbee.

I think the red lock on the back of my bike in the RTW picture was bought when arrived at our first destination. It's something that is quite a high priority after our experience with a bike theft.

Finally, one of the incentives for travelling as light as possible is the weight restriction that an airline might impose. You also have to take into account the box or case or bag that you use to pack the bike. I try very hard to take all my clothing in a backpack or very lightweight carry-on stuff-away bag (Sea to Summit) that will come in at the 7kg carry-on weight limit; I also fudge through the handlebar bag as my "man purse" and it does contain all my documentation and electronic valuables.

I have Excel spreadsheets, too, and I weigh everything I am taking with me and put them in three columns -- bike box, carry-on, and on-me*. That way I can play around with the weight figures until I find a combination that works. I've done that now for five or six international trips, and quite a few within Australia.

* It's not unheard of for people to unpack their clothing and layer it on so they board the plane with just about all their clothes on themselves, so they can come in under the airline's luggage weight limit. I've considered doing it myself, especially with the extra clothes on the RTW trip, but haven't actually had to do so... yet.