Ok – so I had some fun playing with Playdate Caps tonight.
First, I made my own terrible font: https://botsetc.web.app/playdate/BadFont.fnt
It's not great. I didn't spend long on it, and I learned the tool.
But recently I learned about Pico8 and I was rather delighted by their tiny font. It's very small (5-pixels tall), but very readable.
It's available under the CC-0 license, so I figured we should have it easily available to us for Playdate games.
I thought I was going to quickly copy the glyphs into Caps and have a font ready to use, but I started nerding out over the kerning and trying to create ligatures, so I ended up creating a few fonts.
Pico-8
Pico8.fnt.zip (3.8 KB)
I kind of intended this one to be true to the original Pico-8 font, but as I look closer, I think the original font was really more of a mono font, where this one I still allowed for some fairly aggressive kerning (i.e., the letters get tight in on each other, especially some of the symbols)
Pico-8 mono
Pico8-mono.fnt.zip (1.6 KB)
This is actually pretty true to the original. A monospaced font. Lovely, readable, tiny.
Pico-8 plus
Pico8-plus.fnt.zip (4.0 KB)
This is the same as the first one, plus slightly wider # and @ symbols.
Pico-8 ligatures
Pico8-ligatures.fnt.zip (4.2 KB)
This is my favorite, where I went crazy and added a bunch of ligatures (i.e., where letters connect to letters nearby them, like ff, fi, ly).
What do you think?
Did I go overboard on my kerning? On the ligatures?
Do let me know if you try using these fonts and which one you end up liking.
Hope this is helpful to someone 
I had fun doing it!
Josh