We have a few follow up questions 
If this is on one reservation where you change planes but have a single ticket, then any bags you check will go through automatically. (So check as much as possible?). Verify when you check in at your depature airport that the tags are for the ultimate destination.
You'll have to keep your carry on bags with you in any scenario, so travel light.
If you have separate tickets on southwest or even one leg Southwest and one leg someone else, you'll need to pick up any checked bags and go back through security. In that case I doubt you have enough time to do much out of the airport.
Assuming that it was the first case above, there are plenty of poorly paying slot machines at the airport. There are also a couple of lounges for a fee that may be worth it if you enjoy airport lounges for a few hours. That ones I know are in the other terminal though, so you'd need to take the inter-airport train there and back - allow 20 minutes or so for that each way.
Otherwise traveling light and maybe with TSA Precheck you may be able to take a taxi to to the Strip and make it back in time spending maybe a couple of hours there.
The hardest part may be judging the time it takes to walk through a casino if you opt for that.
