Thailand Immigration CAN ask (I not say, you will be asked)
1. valid and genuine passport
2. IF you got a visa issued, a print out
3. Print of the Thailand Digital Arrival Card tdac.immigration.go.th
4. the Boarding pass
5. Proof of onward travel within the period you get stamped into this country
6. Proof of accommodation
7. Proof of finance, 20.000 Thb (40.000 Thb for family) or equivalent currency in CASH
Not every visitor is asked to show all 7 points, it all depends on the Immigration Officer, but IF you get asked you have to show. IT saves a lot of time if you are prepared.
OR show the other comments, special the one, I'm not asked and not specified for me as DTV holder.
Than tell the Immigration Office to shut up and do as you demand but it may have consequences