Merch has been a staple in touring artists' revenue streams for decades, and it's especially crucial for tween-focused pop stars like OneDirection – their fans' parents pay for everything. It can also be a major earner for rock veterans from Iron Maiden to the Who. Those distinctive shirts and caps are always classic.
Potential payday: $225,000 per show
Downsides: Not every touring act can make the lofty $10-$15 per ticket-holder sales of a super-hot amphitheatre act such as OneD. But just about everybody tries.