which leads us to these questions....Are you 20 or 60?
what camping have you done
how minimalist/uncomfortable do you either know or THINK you'll be fine with
I take a full rain gear set, good rain jacket, pants and rain shoe covers, rain helmet cover, this takes up space, but totally worth it. You may not think it's necessary, or rather, think that it's necessary, unless you've spent miserable, wet cold days riding when you didn't have this stuff.....again leads back to your misery acceptance and or real life experiences or not.
so add in camping gear, rain gear and even a small cooking kit, and your rear pannier only setup starts to get filled to the brim.
You'd be surprised how even little clothing additions can make the difference for warmth, comfort. For me it is stuff like a light toque (a beanie), a fleece neck up buff type thing, some thin gloves, warm wool socks, wool blend arm and leg warmers.......
heck I even bring dish washing gloves for those cool, raining all day crap days, if not your hands freeze.
the most important thing is that you practice putting equipment lists together, packing and riding with it to see what works for you, and or your misery acceptance level.
I am 62 and have done a lot of backpacking and tent camping over the years. I have done a good bit of riding but only one week long tour and it used hotels. As I mentioned in my first post I will be doing the Transamerica route next year starting in May, finishing in August and going east to west. One of the hardest things is deciding what clothing to bring since I will be traveling so many states and elevations. Having some extra room is handy. Leg and arm warmers, rain jacket/pants/shoe coverings, some type of warmer jacket or long sleeve layer, beanie are all under consideration.