Mud
His friend wants to be fully prepared for what's to come.
Olive oil. Leaves a great smell and taste for your partner (If you have one).
risk getting a uti.
Just buy lube, it's not very expensive. The pharmacy in my town sells lube for christ's sake. Unless your friend is a puss, he can just go buy a bottle of lube for like $3 and not risk getting a uti.