Possibly of interest to visitors (taken from the TIMATIC travel manual used by all airlines) ... not necessarily what the immigration officer will want!
"Visa exempt visitors older than 12 years must hold sufficient funds to cover their stay (at least THB 20,000 per person or THB 40,000 per family). Proof of funds includes Letters of credit, vouchers, miscellaneous charges orders (MCO) or well known credit cards which are honoured in Thailand.
Visa exempt nationals must have passports with at least one clear half page for immigration stamps."
As we all know, that which is "official" and that which actually happens can differ ...
TLDR : Answer Summary
Visa exempt visitors to Thailand who are older than 12 years must present proof of sufficient funds for their stay, specifically at least THB 20,000 per person or THB 40,000 per family. Acceptable proof includes various financial instruments, but there is a discrepancy as Thai immigration officials reportedly prefer cash upon entry.
