If you ever find yourself in Bangkok without accommodation, grab a tuk-tuk and head towards the Khao San Road, where most self-respecting Backpackers will converge after arriving in the capital. The street is lined with bars which are open 24 hours a day, and you can stay in the rooms above for about £1.50 a night (for a double). As you might expect, the facilities are somewhat limited, but the atmosphere more than makes up for it.
In the surrounding streets you can hear 20 different languages, and the round-the-clock lifestyle and bright lights make it hard to tell day from night. You can also pick up a (pretty dodgy) fake Rolex without selling your home - prices seem to start at about £20 but you certainly shouldn't pay any more than £9 or so.
In the bars, the Sang Thip whisky comes highly recommended (when mixed with Coke: don't drink it neat). Avoid the Mekhong whisky at all costs, as it contains chemicals that make beer hangovers look positively tame.
When you decide it is time to leave Bangkok, you can book cheap minibuses in Kao San Road, from any of the travel agencies or in your hostel, to take you to the airport. Although this is great, just remember it takes a while to get there with the ever present gridlock. However, more important than allowing for time breathing in your last Thai fumes is actually getting on the bus. Make sure you don't rely on you Hostel staff to wake you up at 6am. They will probably be engrossed in some early morning run of the latest Hollywood bootleg video and completely forget to give you a wakeup call as requested. You'll end up with a knock on the door at exactly 5.59am just as the bus is due to leave. If you don't want to end up running down the road carrying your shoes in your hands with your backpack stuffed full of everything you could see in your room, including the bedsheets, you had better find an alarm clock.
Instead you could get a taxi which is pricey, around 250 Baht, but you can just wave one down and haggle. They are still very slow but you can travel at better times of day and they usually have air conditioning. The advantage is getting to the airport and checking in, stress-free.