It’s easy for most people to find a job in America on Labor Day 2019. The unemployment rate is very low; store windows are plastered with help wanted signs.

But for millions of Americans, one job is not enough.

Bridget Hughes, 29, works a regular day shift at a Burger King in Kansas City, Mo. Three nights a week, she also works the overnight shift at a nearby McDonald’s. She makes $10 an hour at Burger King and $9.50 an hour at McDonald’s and, together with her husband’s job at a gas station, they manage to feed their three children and to pay the rent.

“When I thought of my future, I thought I was going to be at football games and soccer practices and cheerleading, when in all actuality I’m lucky if I’m home for birthdays,” Ms. Hughes said. “And my children, they think if mommy is at work all the time then we should have the money. But the reality is that I’m at work all the time and I don’t have the money.”

More than eight million people — roughly 5 percent of all workers — held more than one job at a time in July, according to the most recent federal data. The economy has been growing for more than a decade, but their lives offer a reminder that not all Americans are thriving.