If you are going to be stuck in Bangkok for 8 hours, you don't have many options. If you don't have tons of luggage, I suppose you could hop a taxi over to patpong, but as other members mentioned, most of the replicas they sell there are total crap. You might as well spend your time inside an airconditioned gogo bar knocking back cold ones until it's time to go back to the airport. If it were me, I'd probably just stay in the airport, granted the airport sucks, and if you are sitting in the normal waiting area you are going to be surrounded by Indians and Pakistani travelers who for some reason have a cultural aversion to deodorant. There will be a few tv's set up in the waiting area, which are usually showing a rugby or cricket game.
If you go upstairs you can hang out in the airconditioned internet room, or grab a bite to eat. 8 hours is a horrible amount of time to be stuck in Bangkok, not enough time to get out and accomplish anything, but just enough time to drive you nuts with boredom.