I just bought one of these Boreas bags for UL hiking (the 40L Buttermilk) and I noticed a video on the design of their cycling bags. Since they're minimalist, they won't weigh more than 1-2lbs and they have the trampoline feature to keep them off of your back. Normally, I'll be the first to denounce weight on your back (despite carrying 5-6lbs for a month there!) but the trampoline feature and low price make these a winner. Something that isn't shown in this video is that one of the bags, the Lagunitas, has a waterproof pocket, too.

Reflective, hydration compatible, minimalist, convertible from biking to hiking, and with loops for flashers. Seems perfect for bikepacking: