I know this suggestion is usually met with a near unanimous "don't do it", and I have been among those who strongly advised against it in the past, but I am reconsidering.

Looking at my latest changes to the gear list it looks like I can be pretty comfortable cooking and camping with less than 11 pounds of gear and if I forgo the camera and use the phone camera it would be less than 10 pounds. I figure 4-5 pounds of that can go in the handlebar bag and tarp, bivy, pillow, and sleeping pad can go on the rear rack all rolled up in the bivy.

So I could go with 7 pounds of stuff in the backpack and skip the rack or put the tarp, bivy, pillow, and sleeping pad on the rack and have only about 4.5 pounds in the backpack. Things can be split any number of other ways as well.

I could also just strap the backpack on top of the rack, but I rode with my REI Flash 18 backpack for a number of days on the Southern Tier and found it fine when lightly loaded. I started out using it to carry extra water on the two days that were the longest distances without services, but found I didn't mind it and kept wearing it with a small amount of stuff in it for easy access and the ability to easily take it with me when off of the bike. So I continued to wear it for the rest of the tour. At that point there wasn't much more in it than a couple tubes a jacket and some other small items, but I barely noticed it was there.

Does anyone else here wear a lightly loaded backpack on tour? How much weight do you find acceptable in a backpack while riding?