Do I need to show cash and proof of onward travel for a border run on a multiple-entry visa in Thailand?

With regard to Lopez Koa's post above and thinking about about wishing in the early days in the 1960's-70's one rarely saw a 500 Baht note and a one hundred Baht note was was met with some dismay by street-food vendors or at the market. We learned to carry a lot of coins including 10 and 25 Satang coins. We were literally weighted down with a pocket of change. The BKK bus was 25 Satang then 50 Satang for many years. Guay teo or chao pad gai was a few Baht per bowl. A " fancy" meal was 100 Baht.$100 USD really bought a lot. Lopez Koa could have lived in BKK nicely for six months on $500 USD and in the up country of sleepy Chiang Mai longer.

Inmigration Officials at the borders wanna see cash, no bank book acounts or credit cards.

safer to show bank book account.

In my last visa runs they never ask me to proof money, but I always bring 20k baht, just in case.

I wish 20,000 Baht was only $500 again. The exchange rate is now at the lowest its ever been in years.

its never a good idea to travel with cash, lots of strange people are looking to get your "free". lol

depends on the officer...

if he's having a good day, your smile is enough for him to let you through

if you get a badmood, sexually frustrated, nearly bankrupt one... be prepared...

It i an old sign but still correct. 10k for Visa Exempt and 20K if you come in with a Visa.

Yes you could.be asked for 20k, but highly unlikely

You're not likely to be asked. But it's all up to immigration officer. So, in principle, yes. You need that + proof of lodging.