A customer walks into Casstevens Cash and Carry BBQ in Lillian. (Photo ©Chris Wilkins/Texas BBQ Posse) Casstevens Cash and Carry is a BBQ joint I had been wanting to visit for several years. Located in an old Diamond Shamrock gas station in the tiny unincorporated town of Lillian, Casstevens made the Texas Monthly Top 50 BBQ list in 2008. That’s as good as it gets for Texas barbecue restaurants, unless of course you make their prestigious top 5. Just ask Kerry Bexley at Snow’s BBQ in Lexington. Once they were named top joint in Texas in 2008, life was never…