The CEO should be concerned with events that make it possible for the company to be more successful.
This could be something that directly led to more sales. It could be being part of the team that won a new contract, or the delivery of code that allowed them to release the next version of the software.
It could be something that indirectly led to more sales or more profit. Getting a letter or award from a customer for a job well done is a great thing. It could also be learning a new skill or incorporating a new technology into the products or the workflow. This allows them to add it to the corporate resume.
Managers will have a similar list. They want to know what you have done to help them be more successful. Sometimes they will ignore items that help other managers, but sometimes they see the benefit to these extra projects.
Sometimes going out on a limb, and only being partially successful can also be considered a victory. I have know employees who volunteered for a position that was outside of their comfort zone in order to allow the company to fill a gap. If they didn't fill the position they would lose money. An employee that does this should be recognized.
You should start with listing everything you can think of, and don't worry about an item being too small. Then pare it down before the final submission. You can either go for a small number of grand slams, or a larger number of homeruns. Don't try to say the CEO only cares about projects or skills, they frequently want to see both. I wouldn't include a photo, it shouldn't be relevant to who gets the bonus.
And start working on the list for next year: flag every positive email, note every emergency call, every new skill learned when they happen, not just a few days before the letter is due.