Berastagi is known for its busy markets, hence where else to head to, but to the local markets. Fresh vegetables and fruits produce, flowers and souvenirs - you can get all these from the local markets.
Locally grown passion fruit, known as Marquisa, is probably the most famous fruit. Besides that, one can also get sweet oranges, buah salak, strawberries and mangoes, to name a few.
Was told that you can still get the same fruits and vegetables in those local markets in Medan, but of course not as fresh as those in Berastagi local markets. Well, which is pretty true, where else to get fresher stuffs than where the source is :)