A friend of mine recently asked this from his airline and was told he needed onward travel (within 30 days.) But when he checked in they never asked to see it.
I'd make sure I could buy a ticket quickly on the phone in case they ask.
In my experience, airlines are cool if you have a visa. It's when you try to board without one they may ask for onward travel (within 30 days in that case.)
Similar to other responses. Enter by air: 30 day exempt. Then, extend at immigration OR do a border bounce. I would recommend the Vientiane-Nong Khai border. Very friendly. And you could pop by Udon Thani, which is rather nice. Feel free to PM for more info.
Sorry, it's a plain ticket to anywhere that you can show to prove onward travel withing the number of days you're initially allowed into the kingdom. Whether you use it or not is a different story. You might throw it in the trash and go get an extension of stay instead.