If you feel comfortable enough talking to him about personal things then tell him because he will understand. Men now adays are aware about what women have to deal with when they are menstruating. He will probably be willing to go to the store and get you what you need or at least give you some money to get it yourself. Don't use tampons because your body won't be ready for that, buy pads, you are best off getting the thicker ones that say heavy or over night, there are sticky peel off tabs to keep them in place, and you will need to change them every few hours. Call your mom later on when you know that she is not busy or on the plane and just let her know what's going on and I am sure she will give you some comforting advise.