I don't think I could do a biking (or hiking) trip with carryon only. I've done it for a week-long business trip but that was long before they started cracking down on security. My duffle at the time was about the size you mention and I got some...uh...err..questioning looks then. I bet now it would get pulled. You might be able to do it, particularly if you innocent.

We recently travelled in the US and they were taking the gel/liquid thing seriously. Quite a few people were indignant when their stuff was getting confiscated.

Now, I probably take a compromise. I still pack relatively light in a wheeled duffle (3 changes of clothes, not 2 and I have a pair of "dress" Tevas that double as kicking around and look OK with a skirt). Then I carry on a day pack/fanny pack with books, camera and a change of clothes. I tend to fly out a day early and take the attitude that, if need be, my luggage will catch up, or I have a credit card (as michelem said--I'm not travelling to the 3rd world).

That said, finding clothes wouldn't be my major concern, it would be things like sunscreen and toiletries. I have enough allergies that I have to be picky about what I buy. While I always make a point of going to the grocery store while in a foreign country to see the different types of foods (really, ace, you gotta try it if it isn't on your list!) and while I have visited the pharmacy in both England and Spain, when you don't speak the language, finding a non-allergenic sunscreen can be problematic. I can't carry enough on with today's rules, so I have no choice but to check my baggage.

Good luck, michelem. I stand in awe. But, one thing I learned while travelling to Mallorca--don't try to put the helmet inside your bag. The helment gets hung on the outside, thus not taking either weight or dimensions for your carry on limit.