The journey from Medan to Parapat takes about 4 to 6 hours, depending on traffic condition. As there is no highways or expressways in Medan, travelling from town to town is via trunk road.
Along the journey, one can stop by at Paten Shop, located at Jalan Bandung in Pematang Siantar, to buy local food products, nuts being the main ingredient. There are varieties of this delicacy, with various names, such as Teng Teng, Pong Pong, Tang Tang, Ting Ting, Tong Tong, Pang Pang etc.
Those I bought are known as Ping Pang and Pong Pong respectively. Ping Pang is Bali Nut, while Pong Pong is rice candy.
They allow food tasting prior to buying, hence do not worry that you end up buying something you don't enjoy eating :)