DALLAS – Kathy Doyle Thomas sits at her kitchen breakfast bar, sorting receipts.

The pile to the left is for her travel expenses to a Los Angeles trade show incurred as executive vice president of Half Price Books. To the right are those for Ready Ritas, her margarita mix that comes in team colors and in a freezable, pourable bag — perfect for tailgating.

"This is how I compartmentalize my life," she says, adding paper receipts for 2,500 sampling cups from Sam's and a case of Trader Joe's chardonnay to the Ready Ritas stack.

The second-in-command at Half Price, Thomas is among a mounting legion of Americans with a side hustle — a way to haul in extra cash aside from their main source of income or add a little spice to their lives.

In her case, Thomas, known for decades for serving up mean frozen margaritas from Ziploc bags at parties, wanted to have fun, get hands-on with a small business and spend more time with family.

Sharon Anderson Wright, owner of Half Price Books, thinks the idea is brilliant and isn't the least bit surprised that her longtime friend and colleague is starting a business without missing a beat at her day job.

"Kathy seems to be able to tap an endless source of energy," says Anderson Wright. "She's like me in that we never like to be idle and always want to be doing something. We don't ever get the recommended hours of sleep because there aren't enough hours in the day."

Don't ask Thomas how much money she has sunk into the project. She doesn't really want to know. Sales certainly aren't covering expenses.

"My youngest just graduated, so I kinda think of it as another kid in college," she says. "Everyone says, 'You need to go on Shark Tank.' Why would I want an investor? I want to take my mix and run with it."

She and her three children are Texas Christian University grads and enthusiastic Horned Frogs. So Kathy started making purple margaritas for TCU tailgate parties.

Her husband, Greg Thomas, is a Texas alum, so burnt orange was next.

Now her lineup also includes Texas A&M maroon, and Southern Methodist red and blue. The blue also serves the Dallas Cowboys nation. University of Oklahoma crimson is the most recent addition, which caused a bit of a rift with Longhorn Greg.

There's also a traditional lime green for those who just want easy-to-pour margaritas or who worry about a tinted Kool-Aid-esque smiley face.

Converting the recipe to make a gallon made her very popular with neighbors invited over for testings.

Thomas, Half Price's chief strategy officer, has spent nearly half of her life working in tandem with Anderson Wright, expanding the chain from 29 stores when Thomas got there 28 years ago to 124 stores with $260 million in sales last year.

"I've been in retail forever," says Thomas. "But I've never been in food manufacturing, and it's a whole new challenge for me."

Thomas couldn't have gotten this far even five years ago. GoDaddy hosts her website, and Shopify powers it. "There are so many canned programs out there that a small business person can use. It's amazing," she says.

"You have to be really, really involved. That's the challenging part, but the fun part, too," she says. "I'm learning this whole new business side."