What are the best practices to make a program robust to user error and easily restartable in an edge case?

As part of my graduate school program, I design video-game type experiments for human subjects to go through using Psychtoolbox and Matlab. Despite my best efforts, there's always some problem that will turn up with a user's input being off, needing to pause the experiment, or some other unforeseen event that will cause my code to crash (closing Psychtoolbox in a program usually causes Matlab to fully crash on me). Currently, I write my code in modules for each session of the experiment and these sessions are independently started, but may rely on earlier acquired data in the code.

This brings me to the question of design. How can I design my program to be robust or at least restart-able if some freak edge-case occurs?