Class 1 (Easy): moving water with occasional small rapids. There are a few or no obstacles.
Class 2 (Moderate): small rapids with regular waves. Some maneuvering is required but easy to navigate.
Class 3 (Difficult): small rapids with irregular waves and hazards. More skilled maneuvering is required.
Class 4 (Very difficult): Large rapids that require careful maneuvering.
Class 5 (Extremely difficult): long powerful rapids with confused water makes path finding difficult and scouting from the shore is essential.
Class 6 (Nearly impossible): might possibly but not probably be run by team of experts at the right water level, in the right conditions with the all possible safety precautions, but still considerable hazard to life.

What you should bring?

The fewer luggages you carry, the more you will enjoy yourself. Synthetic fibers are preferable to cotton on the river, as they are light, quick drying and provide insulation even when wet.
For camping and traveling: Sleeping bag and pad, lightweight pants, cotton underwear, lightweight long-sleeved shirt or t-shirt, fleece jacket, toiletries (Including moisture lotion, spare glasses / contact lenses, torch or headlamp with extra batteries, water bottles.
River wear: Secured-fitting river sandals or running shoes are essential in the event of fall off raft. Shirts, or a swimsuit, sarong (for women are recommended when visiting villages, as it covers the legs and doesn't offend the locals), baseball cap, sunglasses with retaining device, sunscreen and leap balm.
Optional items: Small binoculars, camera and film, fishing equipment, Walkman / Discman and tunes, reading and writing material and a personal first aid kit.