Some slight Sarazanmai spoilers ahead!
So Kazuki sings about boxes, Enta about kisses and Tooi about soba (buckwheat noodles). I know these are also the first three chapter names of the novel and most likely what the first three zombies will be (actually I’ve seen people who went to the pre-screening mention the kiss-zombie, I know it’ll be there).
The meaning of kisses is easy to understand. Enta’s in love with Kazuki. It’s not going to be as simple as that though, however I can’t tell what sort of additional issue he’s having with it yet and there are far to many possibilities for me to try to narrow it down.
Soba is trickier to interpret. Since I think it’ll relate to Tooi’s relationship with his brother maybe he has a memory of them eating/making soba together, or something happening at a soba restaurant? As a fun fact “soba” also means “near” so you can make a bunch of puns with that and their names, since Tooi means “far” and Chikai means “close”.
As of for now I feel like Tooi is looking up to his brother and is trying to follow him, even if he’s still just a child and it’s not a suitable lifestyle for him. The gun in his box indicates that either one of them might’ve been involved in a more serious crime, or that they’re planning on committing one.