I've got some old Nashbar Townies (~20 years old) floating around. I might start using them again, except they're not waterproof and lugging them off the bike is a pain. Seriously thinking about just leaving them on the rack and hope they don't disappear.

i'm thinking about going this route

www.donkeyboxx.com

If I had a mixte frame or didn't have to wheel my bike through the front door, I'd be real tempted to go with the donkey boxx.

I know from experience that my favorite backpack will fit inside one of the Townies with a small to medium load, but won't if it is filled to capacity.

I like large backpacks. I once brought home about 70 pounds with one of mine. 66 of that was a bag of cement.

They put weight on a person's spine. If cycling is the main form of exercise, the spine doesn't do much load bearing, and will tend to lose mass as a person ages.

I use an Ortleib Bike Shopper, which I guess is a grocery pannier. I like the fact that it has a zip-loc style closure rather than a roll-top like the Backrollers do. I also find one is enough for a load of clothes + some random groceries.

The Donkeyboxx looks cool for me right now. I have a rear rack on the way to mount one on. Can I just get a single box for one side or is weight distribution a worry that I should get one for each side and split the load? It doesn't appear that they would be far enough apart to make a noticeable for a novice that won't be pushing any handling issues to a limit.

I am pretty close to fabricating my own kitty litter bucket panniers... or at least one for starters, as I am stealing mounting hardware from my old panniers to do it. They should be a lot more stable than the Nashbar Townies I have and don't use because they're too floppy.

I think the have a payload limit of 30 pounds. If you have that much, you might want to split the load. You probably won't notice anything under 15 pounds or so when using only one while riding. Parking, standing, or walking your bike with that load might be a different story...

I lack the DIY skills, the tools, the money for said tools, and felines, otherwise I would've probably tried 'em out by now.

I have a chinese produced "Roswheel" messenger bag that clips to the rack but has a large shoulder bag and handle for the rest of the time. It's not water proof but its rain resistant and large enough that I carried 2 gallon bottles of cleaner home once and it still closed mostly(expansion zips like luggage). So far no complaints for the daily commute of 10 mi of hills.

Tools: I'm a homeowner, so check.
DIY skills: I have combined generations of international kludging experience... and an engineering degree.
Felines: Nope, Mrs. A is allergic. But the neighbors across the street have two.

Like I said, the hardware is coming off of panniers that fell off one too many times and are pretty messed up, so these are going to be pretty much cheap as free. Too bad that won't work for you, though.