> you can go to an airport, which has never closed, and buy a ticket in cash

This has not been true for some time. Ticket counters require payment cards.

I asked about purchasing things online because it's not safe to shop in person at the moment.

Interesting, I remember being able to pay cash a couple years ago, but now I see most airlines stopped accepting cash, ex: https://www.dallasnews.com/business/airlines/2020/07/07/sout...

Even Amtrak is now not accepting cash anymore:

https://www.amtrak.com/purchase-train-tickets

Looks like the only option left is drive a car and fill up at gas stations which accept cash (for the time being). I'm not super familiar with EV charging stations but I don't think I've seen one that accepts cash, if that's any hint as to where we are headed.

Dark times