The first programs I wrote were on my graphing calculator for high school.
I used to write programs that automatically solved some maths problems and just before the exams people were begging me to transfer it to their calculators. This got me a lot of free lunch.

There's a plug in the calculator that is used to transfer data from one calculator to another.
Unfortunately I didn't have the adapter to connect it to a computer so I had to type everything on the calculator keyboard which took a lot of patience.