Kaosan Road is popular among backpackers and western tourists. Here you can shop, eat and sleep without spending a fortune. Around Kaosan there are a lot of western cafes, burger shops, pizzerias and the like. On the street you can buy driver's licenses and other ID cards. Of course that's illegal, do not even think about it.
The flower market is located on the southern side of Thanon Chakraphet Street, here you can find all the flowers of Thailand. Flowers are put together to form long chains as an offering in the temples.
Bangkok is famous for its delicious street food. Unfortunately, the military government has banned the small food stalls on the roadside. The often illegal stalls have to move to markets. Street scenes like here in Chinatown (photo) will soon be history. One reason for the ban on street kitchens is, that pedestrians have too little space. But it's probably also about money, because the street food stalls pay no taxes.
Padpong is the most famous district of Bangkok. The "Padpong Market" is the place were you can get fake watches, bags, and other fake branded goods. It is illegal to import these goods into almost any other country. This is also the place where the wild nightlife of Bangkok happens, with gogo bars, prostitutes and ladyboys.