[cturner]

Yes, this space is high on tradeoffs.

With plenty of source power, pixel grids are flexible. You can construct these from LEDs and paper, https://www.youtube.com/watch?v=QWGoC-9z2Qw. Or chain together 16x2 displays, or use flip-dot displays if you can source them.

If you are low on power, morse-code over a single LED would go a long way - low on equipment cost. Audio output and radio could also be decent low power outputs.

Seven-segment displays are workhorses. Restrict the interaction to hexidecimal characters.

Other obstacles for post-apocalyptic computing are power and storage.

For power - generation itself could be ok from a bicycle. But you need a way to buffer the power.

For storage - FeRAM should be a good option. Will not decay like conventional disks, so long as you repopulate it every few years.