A set of Ortlieb Sportspacker (optional Plus) can be secured to most any rack, and it's nicely sized for a few changes of clothes, toiletries, and room for an extra water bladder if you're riding where you can refill every 25 miles.

I agree about the Ortlieb panniers, although you may want a larger size. Any Ortlieb rolltop style pannier is an excellent choice and, once setup properly, their mounting system will stick to your rack no matter how bumpy the road surface.

As to the mirror, you don't say if you're using bar-end shifters. If not, there are several choices that work. Google bike mirrors and choose one with a large mirror surface. When I had bar-end shifters, I initially used a Blackburn mirror which attached to my brake housing. I later switched to a helmet mounted mirror (Efficient Velo Tools Safe Zone Helmet Mirror) which I like best of all the mirrors I've used. It's expensive (~$40), and takes some getting used to, but provides a consistent clear view behind you.

In the end, it's a matter of preference. I'm sure others here will chime in with their thoughts.

Safe Zone mirror is well worth the $$ IMO.

I have seen bikes using a mirror mounted just under the drop bar brake lever
often this one Also from Ortlieb's USA distributor..

If you don't have bar end shifters, the Sprintech bar end mirror has worked well for me. The view on bar end mirrors isn't that great but I've tried helmet and glasses-mount mirrors and always end up breaking them pretty quickly. The Sprintech has survived my rough handling very well.

Every time I tried mounting a mirror on my handle bars I would get so much vibration I couldn't see anything. For those recommending the bar end types, How do you stop the vibration?

indeedee

the Arkels aren't super tough, so you just have to use common sense with packing and sharp edged objects, but they are super light, completely water proof and as you say, have a smaller profile.
Only downside is not easy on, easy off, but for cc stuff, generally you'll have the bike with you in a hotel room, so even easier to just leave them on.

Snow--how about a photo of your bike?

ultimately, for rear panniers, there are tons of good ones out there, I personally put an emphasis on waterproofness, and there are many models out there by various companies that will be fine for your use.

I can't remember snow if you have toured before? I guess not if you are looking for panniers. If there is a chance that you will use panniers for commuting etc in the future, it makes sense to get some well made, easy on easy off panniers that will get used by you in the future.

Agree on the large bags. I replaced my Ortleib Backrollers with Ortleib Frontrollers. Even for camping-tours. Just did a CC trip down part of the Katy, and my gear was in a handlebar roll, with a soft-sided cooler strapped to the rear rack. Fortunately my bike has all kinds of gear storage options including a frame bag and fork cages, but that stuff usually doesn't get used unless there's camping involved. For credit card touring, small panniers or a handlebar roll seems to do the trick. Maybe both if the weather might turn cold because cold weather gear takes up more space.

My Trek Domane has an elastomer doo dad where the stem meets the frame and it dampens a lot of the road buzz - since I've only used a bar end mirror with that bike, vibration in the mirror hasn't been a problem.

Pics or didn't happen.