We did the Grand palace (amazing) and Thai Kick Boxing. We paid £10 for the front row seats but the "cheap" seats looked much more interesting as they seemed to be having so much fun up there, behind their wire mesh screens.
Tuk Tuks are an experience not to be missed but they will rip you off, probably to the tune of £2 or £3 so don't let it worry you. Meter taxi's are best value and air conditioned but not as much fun.
Patpong night market is an experience too. Go into one of the bars and have a look at what some of the girls can do with ping pong balls, ribons, mice 😯 etc. If they offer you a balloon, politely decline before the girl starts shooting "air" powered darts at it.
Generally be aware of what and who is around you (as in any major city) and you'll be fine. We've been twice and never had a problem there.