x2 on the poncho. No pack cover needed, can serve as a tarp/shelter, something to sit on when you take a break. If he refuses all emergency gear, hike if you're 100% sure of good weather. In the past, if I've hiked with someone and they blew off my suggestions for being somewhat safe and prepared for the conditions, they got blew off themselves. Don't ruin your hike because someone has a problem being reasonably safe and sane.