For such a small town Midoun has plenty of stalls selling souvenir goods. Midoun is very close to Sidi Mahres where many tourist hotels are located so I imagine a lot of visitors come here to see something of Jerba other than the beach and a four star hotel. Many of the shops seemed to be selling the same old souvenirs. I'm surprised there are so many of them doing business.
The souks have the stuff that will typically be sold in places where herds of tourists come.
What to buy: The shops sell small dromedary-toys, chess games, water-pipes, groceries, tea, ...
What to pay: Too much anyway if you are not speaking tunesian of arab :-)
Places such as Midoun have their own small markets selling handwoven rugs, terracotta pots, spices, copper or brassware and the gentlemannered Berbers are a pleasure to meet.