At the market at Nuku'alofa things sold are specific to Tonga. There may be some fruit and veg but the thing you see most, and which you won't see anywhere else, are mats. The are called ta'ovala and are to be worn during special occasions (you can see them in my other entry, Tongan attire). For example to church, or at a funeral, or at a concert for a crew of an American ship that came to the key. Women can sometimes wear a smaller thing called kiekie.
Normally they are only worn at special occasions but one can see a kiekie seller wearing one, just to show what it looks like.
One can buy ta'ovala and kiekie, but also other things made of reed (as I assume, I am not quite sure what they are made from), like fans (with the name of Tonga written on it, so they are probably for tourists who sometimes come here).