The travel rewards game tends to benefit those who have the most flexibility—and no one is more flexible than a party of one. A passenger sleeps in a United Airlines' Elevated Polaris seat.Credit: United AirlinesThose stories you hear about someone booking a $10,000 business class seat for a fraction of that in miles? More often than not, that person is traveling alone.And the advantage doesn’t stop at flights—many loyalty perks can, in fact, fa…