I often do this on flights, and in addition to solving "puzzles" you can always try to build a well-defined system from scratch. For example: - A JSON parser

I often do this on flights, and in addition to solving "puzzles" you can always try to build a well-defined system from scratch. For example: - A JSON parser (bring the BNF from http://json.org/) - Simplified Lisp interpreter - Forth compiler (for example: https://github.com/JohnEarnest/Four.Ps) - Emulator for a simple CPU or MCU (6502, 1801, etc- bring a datasheet) Projects like these are not "practical", as everything here has been done before, but great learning experiences.