There's no reason to buy anything without getting points for it. Brian Kelly, whose website, thepointsguy.com, offers tips for maximizing miles, has a trick for doubling and tripling that purchasing power. "I'll buy a gift card through an airline website" – Delta's skymilesshopping.com, for example – "using my airline rewards credit card. So I'm double-dipping. Then I'll spend the gift card through that same site. That way I'm getting three times the miles."