Depends on the mileage. With St. Louis to Vegas, they’ll probably offer snack mix and drinks (and probably seconds if you ask for it). To Hawaii, they’ll likely come around with two snacks/beverage services. On the flight to Hawaii, they’ll offer you seconds if you request it. This all depends, though, on turbulence as snack/drink service can be suspended if the captain deems that it is unsafe for flight attendants to be moving around in the cabin.
Also, I would recommend bringing snacks, a sandwich, or eating in Vegas or STL before your flight since Southwest planes are only stocked with drinks and pouches of snack mix - nothing like a full meal onboard.
