Definitely include the following:
bottled water
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.
These are just a few items that come to mind.