Beware the living bread.
It's probably reading too deep into it because becoming toast might just be for the pun, not to mention there's lots of actual dead skeletons of Omori's friends across Headspace, but the idea of becoming toast being a kiddy way of Sunny trying to repress and wash over the idea of his loved ones dying by having them become toast instead is pretty sad. After what happened that night. Even if this is wrong, I still think something like that is being applied to this room specifically because of who and what the toast turns into.