We have a very successful farm shop near us, they started off with a yearly second hand book sale about 10 years ago that grew and grew, now they have just built a lovely big shop with a cafe etc, they have a map of all the local produce they sell, honey, jams, cakes, soaps etc all bought in from the surrounding villiages, they hold various events through the year, open days, demo days, nativity evening etc, they have freezers full of home cooked food made on the premises, as well as thier own meat, eggs and veg, i guess you are only limited by your imagination. But I would say that local produce is the most important for me, there are lots of people out there making/growing things that would love an outlet opportunity. Good luck in your venture