some type of snack (nosh, fruit, pretzels, mints) clear directions to the shul (auf ruf) and/or your home, as well as a hand-drawn map to the homes where they will be sleeping, with all street names clearly marked. Maybe a Jewish magazine or paper, some type of reading material.
It’s nice to write a poem or nice note of welcome to them.
also to include a printed schedule for shabbos indicating times for candle lighting in your city, davening times, zman krias shema, when and where the seudos will take place, etc.
Speaking from a guest’s point of view – If I would ever find Advil in my welcome package, it would make me wonder if there’s something about the caterer that I don’t know about but should!