If it's true that an army travels on its stomach, will better snacks keep passengers loyal to one airline?

Delta Air Lines is rolling out new free snacks for customers in the main cabin, including brand-name yogurt bars and pretzels. Some will come in larger portions than before because, Delta has figured out, that's what customers crave.

The menu move comes about a year after United Airlines brought back free snacks by offering noshes like stroopwafels - a gooey Dutch confection - and better coffee. Earlier this year, American Airlines restored free snacks on domestic flights.

Airline executives say they're focusing on both big and little things in the battle for customers.