There are various weekly markets in the area.
I would say the biggest and best one is at Cambrils
Followed by La Pineda and lastly Salou.
There are various items for sale. Lots of shoes, fake designer handbags, denim and lots of underwear stalls. The market at Salou seems to have more knicker stalls than anything else.
Some of the stalls will not barter very much - these usually have their prices clearly marked. The ones that have not got their prices marked will generally barter with you and you can pick up an even better bargain.
What to buy: Some of the shoes are a real bargain.
Bags are another bargain especially if you steer clear of the fake designer ones (which can be a bit tacky anyway)
The underwear is reasonably priced but ladies beware, if you are looking at bras, the market holders do have a habit of trying to fit you with the bra over your clothes as you are standing by their stall. It can be a bit embarrasing.
all along the center of salou there are dozen of shops to stroll around and do some shoping. nothing so special. just normal ones like many others at a vacation site.
What to buy: recuerdos as they say in spanish are the main items to buy. a t shirt, a post card, etc.