Thanks for all of your opinions.
I'm definitely getting two, new, identical computers. The old ones are working just fine, and 22 years with only two minor problems is a good track record for ThinkPads.
One displays lyrics or head chart, the other runs mp3 files. Really, really light duty for a computer. The old XP computer that refuses to die does both of these jobs simultaneously, with no problem.
I don't need blazing speed, but I do need reliability. ThinkPads are reliable, plus being black and small, they are not distracting on stage. I don't want networking, office, malware, or anything else on the computers. The less I have to depend on, the better my reliability score is. After initialization, they will never go on the Internet.
We were completely out of work for 2 years due to COVID, and last February, it seems like people have been trying to make up for lost time. So since we are gigging a lot, it's time to reinvest.
I have two EV-ZLX15P powered speakers, they have been discontinued, so I bought a spare, just in case one goes down, I can still have two while the first is being repaired.
After COVID most of our gigs are outdoors. Often, that means in dimly lit situations. I have a little USB LED light on a gooseneck, but I think a backlit keyboard would be better.
Why the flash drive question?
The idea of running off flash drives is for convenience, and nothing more. It would save time dragging and dropping to the HD on two computers. I was thinking something small like a Samsung fit.
I have identical files on a flash drive anyway, which I bring to the gig, for more redundancy. I also bring a working, inexpensive computer to the gig, in case both computers die at the same time. Hopefully the line conditioner/surge protector would prevent that, but -- just in case.
Mrs. Notes and I started this duo in 1985, and have never missed a gig for any reason at all. Equipment redundancy is a way of life. I use a power conditioner, take care of the gear, and it serves me well. Two minor computer problems that didn't stop the show in 37 years, thanks to redundancy, is a good track record.
BTW, I have dozens of flash drives. I mainly use them for sneakerware to transport files from one computer to another. That's light duty, I know, and I've never had a failure ----- yet.

Thanks for your input, I'm getting a little cooler on the flash drive option.
Insights and incites by Notes ♫