The Someday Suitcase — Corey Ann Haydu

Clover and Danny are the kind of best friends who make each other even better. They're so important to each other that Clover believes they're symbiotic: her favorite science word, which describes two beings who can't function without the other. But when Danny comes down with a mysterious illness that won't go away, the doctors can't figure out what's wrong with him. So Clover decides to take matters into her own hands by making lists -- list of Danny's symptoms, his good days, his bad days.

As the evidence piles up, only one thing becomes clear: Danny is only better when Clover is around.

Suddenly it feels like time is running out for Clover and Danny to do everything they've planned together -- to finally see snow, to go on a trip with the suitcase they picked out together. Will science be able to save Danny, or is this the one time when magic can overcome the unthinkable?