I almost always bike with my deuter exp race whatever its called and generally it weighs a ton cause I have a spare everything and 3 liters of water (I don't put water bottles on the frame usually)... and I tend to bike by this farm stand and start shoving butternut squashes and things in it... and yeah, I ride with it for hours, I'm used to it and doesn't bother me.

But... if you did the aluminum seatpost + seatpost mounted rear rack... You can bungee your sleeping pad/sleeping bag/tent for probably less than 10 lbs of weight. Stash the sleeping bag and tent in a drybag. Depending on the season, a down vest and maybe down booties you can squeeze little are handy for around camp. But sounds like you do enough lightweight backpacking that you probably don't need hints on what to pack.

If you want a lighter stove, you can do a pepsi can stove. The rest of whatever you need in a backpack.

If you need a little bit more storage, you could put a handlebar bag on the front if you don't have carbon handlebars (you probably could put one on with carbon handlebars, just don't put too much weight in them.)

costco sells some light solar rechargeable flashlights, 2 for $20 that I think are great. I keep 'em strapped to my kayak deck when kayak touring, or just in the outer mesh pocket of my backpack when backpacking or biking. More than enough light for at night when combined with a headlamp in case you need more light.