Brand new hundred dollar bills for exchange. Worn, marked or folded bills are typically rejected by money exchangers. Bring HALF the amount of clothing you would typically bring (clothes are CHEAP). Also, good walking shoes and smile will get you almost anywhere.
I’ve recently retired from working in a surgical setting - seen MANY people in an ICU, intubated, “faking” their sickness - just so they could get the benefit of having a tracheotomy. The nerve of those people!!!
I took a train to Hua Hin several years ago. Though it was a bit of an adventure, it was Slow, scary (I was in fear of derailment due to someone stealing the track for scrap) VERY bumpy, and had no air-con. I won't be doing it again.