If you're a software engineer, memorizing an ASCII table (particularly the hex numbers of each character code) is definitely helpful. If for no other reason than so that you can read things that are randomly written in binary without having to consult a table.
Something not really otherwise terribly useful that nonetheless helped me keep my sanity: learn how to convert to base64 in your head. At work, we had really boring 8-hours-a-day training for a couple of weeks. To pass the time, I came up with random strings to base64 encode in my head. "Hat is 48 61 7a. The first six bits are 010010 which in base64 is an S. The next six bits would be 000110 which in base64 is G." Etc. I'd write down the base64 strings character by character as I derived them and then check my results for errors when I got back to my desk.
Mom wanted me to go into music performance. I went into computer science both because "holy shit how cool is that" and to get out of music performance.
My alma mater had three computer departments: CSC/CompSci, CIS/Computer Information Systems, and Graphic Design. I've never been artistic, really, so I didn't have a lot of interest in Graphic Design. But I didn't know the difference really between CIS and CSC going into college.
I went to the head of the CIS department to ask about the difference and he was like "CSC is about building the plane, CIS is about flying the plane." Misinterpreting that to mean CSC was about hardware and CIS was about software, I thought I wanted CIS. When I met with the CSC head, he met with me in a little lab in the CSC department. And on the shelves on the walls, there were robotic coin sorters and Lego robots and stuff. And that's basically when I realized the CSC department was my people.