Sougia is no shopping paradise but the shops of the village will provide you with most of what you might need on your holiday.
There are two shops that could be called minimarkets and sell many things from food items to books and articles of general use. If people in Sougia often need it, they will generally have it.
Another shop, Irtakina sells beach goods, clothing and other non-food items and of course there is the shop of Roxanne with bakery items and snacks (and she opens before everybody else in the morning - very useful if you want a coffee and a light breakfast snack before catching the early bus). Roxana who speaks English and fluent German is also a great (and willing) source of information on just about everything in Sougia.
If you need more specialized items, like from a chemist, you will need to go to Kandanos or Paleochora.