A trunk novel is an unfinished or unpublished novel. It could be a work in progress that the author hasn't completed for various reasons, like getting stuck in the plot or facing distractions. Sometimes, these trunk novels are later discovered and may be revised and published if they are considered to have value.
One bride trunk scary story could be about a bride who put her heirloom wedding dress in a trunk. When she opened it on her wedding day, the dress was all torn and shredded as if some unseen force had been angry at her wearing it. Another might be a story where a trunk that was supposed to hold the bride's trousseau was haunted. Every time someone approached it at night, they could hear strange moaning sounds coming from inside, as if a spirit was trapped within the trunk, mourning for a lost love or a wedding that never happened.
Well, it could be some magical items like a self - cleaning quill. You know, for Harry to use in his studies at Hogwarts. It might also have a cloak that has some special property, perhaps one that can change colors according to Harry's mood.
Some might be inspired by real events. For example, there could have been instances where old trunks held unexpected and spooky things. But many are likely just fictional tales passed down through generations to add a bit of mystery and spookiness to wedding lore.
It could be Hagrid. Hagrid is always looking out for Harry and giving him things. He might come across this special trunk during one of his travels in the Forbidden Forest or in some wizarding market and think it would be perfect for Harry.
There could be some of his parents' old school things like their Hogwarts robes, wands (if they were allowed to keep them), and textbooks. Maybe there are also some love letters between his parents or photos of their time at Hogwarts.
Well, 'The Girl in the Trunk' being a Kuroshitsuji fanfic, it might explore unique storylines within the Kuroshitsuji universe. It could focus on a girl's journey or adventure that somehow involves being in a trunk. Maybe it's a mystery - like she's trapped in there for a reason related to the dark and complex world of Kuroshitsuji, perhaps she's a key to some hidden plot or has some special power that makes her situation important.