Memory’s Legion: The Complete Expanse Story Collection by James S. A. Corey
This collection of short stories and novellas isn’t necessary reading if you enjoyed the Expanse novels, but it does flesh out some of the characters, both main and secondary. I think my favorite story was probably “The Churn,” a dark and disturbing tale from Amos Burton’s younger days, followed by “The Vital Abyss,” which explores Paolo Cortázar’s research into the alien protomolecule.