Can I use a USB stick to store cache?

Is it possible to (easily) have my computer store cache files on a usb stick, and if so, how?

You can create a symbolic link from the Caches directory to your USB drive.

1. Move your Caches to your USB APFS volume or remove the folder.

2. Create a symbolic link from Caches in your home directory's Library to the location you moved your caches to.

   ln -s ~/Library/Caches /Volumes/usbname/Caches
   

   How can I create a symbolic link in Terminal?

You will need to ensure the name of the USB drive does not change and you do not turn on your Mac without the drive connected. Be prepared to experience slowness as the speed of the USB drive will almost certainly be much slower than the internal SSD speed.