Print film is fairly inexpensive and widely available throughout Thailand. Slide films, especially Kodachrome, can be hard to find outside Bangkok and Chiang Mai, so be sure to stock up before heading upcountry. Film processing is generally quite good in the larger cities in Thailand and also quite inexpensive. Kodachrome must be sent out of the country for processing, so it can take up to two weeks to get it back.
Pack some silica gel with your camera to prevent mould growing on the inside of your lenses. A polarizing filter could be useful to cut down on tropical glare at certain times of day, particularly around water or highly polished glazed-tile work. Hill-tribe people in some of the more-visited areas expect money if you photograph them, while certain Karen and Akha will not allow you to point a camera at them. Use discretion when photographing villagers anywhere in Thailand, as a camera can be a very intimidating instrument. You may feel better leaving your camera behind when visiting certain areas.