Airlines continue to find new services to charge ancillary fees. The world's largest airlines raked in $36 billion last year based on these fees, and the extra charges are not stopping any time soon. United recently unveiled a priority boarding fee that also lets fliers whiz through security, while Southwest charges fliers to stream movies on devices. "Everyone in the industry is starting to dabble with fees," said Amy Lee, senior analyst at Travelnerd.com. "Even the budget carriers are getting into the game."