Took a flight from San Francisco International to Las Vegas on Southwest. I never fly this airline but only for work as my company books me with Southwest as one the cheapest to fly around on Government rates, I guess. Their boarding system has group numbers as most airlines now do, but with no assigned seats. You get on board to seat wherever. If you’re group C (A & B groups already boarded), you have very little to zero chance of keeping your carry on except under the seat as all overhead bins will be full by the time your turn comes to board as it happened to me on that flight. As to the no assignment seat, I like to have my seat assigned. The airline onboard service is very limited - a pack of peanuts and a cup of soft drink and that’s it. They do not even use cart. The flight attendants go and ask every passenger and write the orders on a clipboard. I am not sure if they have travel class. It is just that some people get to board first depending on loyalty status. Southwest flies the smallest Boing 737 - rather old machines, you’d notice as soon as you board. I have to admit, though, that crew was very polite and friendly contrary to most other US airlines which are not. I’ve noticed some passengers do not deplane as they use the same aircraft to continue onto another destination - something like a bus service. Oh yeah, I as soon as at the gate and people started to leave the plane, the flight crew turned into janitors with rubber gloves and begun picking up trash. I mean, how cheap this airline can get to not even hire proper cleaning staff?