If you use the company car for a side hustle in catering, then that perhaps gives the company the right to fire you or charge you for damages. However, they do not get to claim any intellectual property (recipes you invented for your catering side-job).

I agree with that. In the pen example, they should bill you for the wear and tear on the pen (ball bearings and ink aren't free). In the computer example, same deal. Figure out what a flash memory erase cycle is worth, figure out what bringing the CPU out of its lowest power state costs per minute, figure out how many of each were used, and send an invoice!