You can reuse the screen with an LCD driver and USB touch interface board. It can also hold a window open. Other than that, unless you're a collector or a museum, nothing.

It's very cool to get old things working

Battery is probably worthless, so probably not much. Not even sure what version of iOS it can run. Doesn't look like PostmarketOS can run on it yet.

You miiiiight be able to get a Linux Kernel booting, but not sure where you can go from there because there will likely be no other hardware support for the touchscreen or media devices: https://github.com/SoMainline/linux-apple-resources/blob/master/HOWTO.md

Here is one of iPad reuse projects

And here is a crazier and thorough project on replacing internals

TBF I considered using my old iPad2 as in-car navigation or just as permanently-on weather display or picture frame. (If battery doesn't swell from being on all the time)

As somone who used to jailbrake iPod Touch 4th and 5th gen, not much. I doubt much has changed since then. I doubt iPads are in a much better state either.

If you can find the old .ipa app packages, you could use it as an offline devices for old apps and games that no longer run on newer iOS versions.

you can install unofficial ios 6 on it. run old apps, etc

Use it as a coaster