Nice try, kid always wears athletic shorts, and they usually don't even have pockets! I can force him to wear cargo shorts, but was hoping for a better idea.
I say pockets too. My DS16 won't even buy athletic shorts (or any shorts) unless they have pockets. Most of them do. We have rarely run across shorts without pockets. If his don't have any - then go and pick up a few pair before the trip. Cargo shorts are best and I usually have DS wear them on vacations just because they look better in pictures..
He's 15 - I would tell him to figure it out himself. If he doesn't want to wear shorts with pockets, he'll have to carry it, bring a bag, or not take it.