It was effectively a portable computer that I was allowed to use and play with in most classes.
Started with TI-BASIC, then discovered ticalc.org and the shell and assembly programming hacks, games, and home brew transfer cables.
It effectively started my electrical engineering and computer science career.
I know I’m not alone.
I'm kicking myself for not saving the game code I wrote for some of those early games. They weren't very good, but I'd love to see the code, despite the horrifying spaghetti that it was.
Authoring programs using the buttons on the calculator was not fun.
I eventually made enough money from "donations" from people to buy a proper cable, which did improve my DX quite a bit. The hacked up parallel cable wasn't the most reliable...