Add to that list, virtual memory paging files which can get quite large if you have a lot of stuff running. Seeing as you have 256 GB of storage, I'm going to take a guess you might have 8 GB of RAM on a base model Air. If this is true, you could easily generate big VM files the system uses to temporarily park stuff you have open that doesn't fit into RAM.
If you want to see the VM, you can use the Go to Folder command in the Finder and paste in /System/Volumes/VM. But do NOT mess with the files or you'll crash your machine immediately. They will get deleted automatically when you restart. I've got about 8 GB worth of VM files sitting there as we speak.