The national average for a gallon of gasoline has been ticking up since the start of the war with Iran. In Killeen, Texas, it's up $1.28, which comes to about $90 more every month for Charles Rice to fill up his truck. 

"$3.96 instead of $4.12 or $4.20 or what have you, so that's what brought me in here today," Rice said while filling up at Casey's General Stores. It's the nation's third-largest convenience store chain, with nearly 300 locations across 19 states. Two-thirds of Casey's locations are in towns of 20,000 people or less.

Store visits at Casey's are expected to jump 20% Memorial Day weekend, the kickoff of the chain's 100 days of summer, said Casey's CEO Darren Rebelez. 

"The consumers have been hanging in there, and we tend to price our fuel at the lower end," Rebelez said. 

Before the Middle East conflict erupted in February, the national average for a gallon of gas hovered just below $3.

Around the country, a gallon of gas now costs an average of $4.50, up more than $1.50 since the war started, according to AAA. And in a May 12 forecast, the U.S. Energy Information Administration estimated that retail gas prices will average $3.88 per gallon over the rest of the year and $3.62 per gallon in 2027. 

Consumers are making some trade-offs in other areas due to the rising cost of gas. Sales of Casey's self-branded snacks, which sell for about a dollar less than national brands, are up. 

"People normally want things that are going to be a little bit more affordable," said Tiffany Bishop, a customer. "Especially when you have kids that want to pick up snacks." 

Rebelez said a lot of consumers will come to Casey's because it's a more affordable option.

"When we get into times like this, where you know, budgets are stretched a little bit, we're viewed as a better value option," Rebelez said.