Originally Posted by
Carbonfiberboy
We tour with panniers and also use an REI Flash 18 ultralight daypack. Originally we were going to use it on the rack, as you suggest, but wound up using a compression sack there and used the Flash for temporary overflow and day hiking during a tour.
I have done similarly.
BTW, I love the Flash 18. They redesigned it and I have not had a good look at the new version, but my older one is a great little pack.