How do you keep the files you are working on in your head when programming?

I find that this is the biggest pain point for me. When I am working on a task, it usually ends up spanning several files. And I just don't have very good memory.

I struggle to remember if I had some new variable in the Logger or the Worker, etc. It's usually trivial to see the list of files I'm working in and check between a couple, but I'd love to know if anyone has a memory palace kind of technique they use for programming.