If you're struggling to think of things which you're especially proud of - don't beat yourself up, ask for help from your previous coworkers and connections. It's a simple email to send them:

To: Friendly Coworkers
From: You!

Hi, I'm completing a Manual of Me, and need to list three things which I'm proud of from recent years.

Can you think of any projects we worked on which were especially fantastic, and that I should share with my future coworkers? Why do you think these were special, and what did I bring to the project to make it even better?

Thank you so much for your help!