Overnight Bag
A small bag that a woman brings to a man's house when she plans to spend the night; it usually contains a change of clothes, accessories, personal toiletry items and miscellaneous feminine products. When a woman announces she's bringing an "overnight bag," it's usually implied that sex will be had. Some associate overnight bags with casual sex.
She direct messaged him back, her reply to his invitation to spend the night : "I'm not really into casual sex. Yes, we went on 'a date,' but I just don't see myself packing an overnight bag and coming over there to stay the night, when we really don't know each other."