You come to Hong Kong mainly for shopping. You enter from Shenzhen Bay Port and go to Tuen Mun or Yuen Long. Take B3X to Tuen Mun downtown and B2 to Yuen Long (the driving time is about 15 minutes).
I would recommend going to Yuen Long, because shopping places are concentrated. You can buy everything you want in a main road and an education road parallel to the main road in Yuen Long.
Chinese medicine supplements can be purchased in Weiyuantang, Beijing Tongrentang and Huaruntang (recommended), and other Chinese and western medicine supplements can be purchased in Wanning and Watsons.
At present, there are not many commodities that are restricted from being taken out of Hong Kong, with the focus on "infant formula". Take B2 to Yuen Long and pay in installments. Pay 8.5 yuan first when you get on the bus, and then pay 3.5 yuan when you get off the bus (after the Hongshuiqiao station). If you use Octopus, you should brush it once when you get on and once when you get off.