In Yuen Long, if you are looking for something, it's a good bet that you'll be able to find it along Castle Peak Road (FINGER'S CROSSED!). Walking down from the Yuen Long Plaza, Castle Peak Road is lined with clothing shops (nothing fancy like H&M or Gucci, but your basic Balenos, Timberland, Crocs, Maples, etc), bakeries, electronic shops, appliance shops, restaurants, jewelry shops, cosmetic shops and the like.
***Walk with me along Castle Peak Road***
During the day, you can find little vendors that sell fruits, vegetables, knick-knacks, electric fans (which everyone seems to have hanging around their necks these hot days), towels, t-shirts, nail clippers (who'd of thunk!), and even dried fruit.
There is also a kid zone (a.k.a. The Playhouse) up above the Pizza Hut at the Yuen Long Landmark, which might be a great place to take your kids when you need something for them to do this summer. Inside the Yuen Long Landmark are a few restaurants (Pizza Hut, e.g.) and also DSC (the furniture and appliance center).
A handful of shops open up quite early, before 10 am, as there are a lot of mainland tourists who stop by Yuen Long.
There are also all the main banks that are found along Castle Peak Road: Hang Seng, Bank of China, Fubon, Citic Bank, HSBC, Dah Sing Bank, Standard Charter...
Fun Fact: Back in the day, Yuen Long was know for their "Wife Cakes." The original shop (or the shop that made them famous) is right on Castle Peak road, as well. These guys open mondo early, so, if you don't like the crowds, stop by in the mornings!
All the buses also run through Castle Peak Road. If you need to catch the 968 into Central, you can find the stop along Castle Peak Road. If you are heading into Mong Kok, catch the 68x along Castle Peak Road. If you are heading over to Tai Po, you can catch the 64K off of Castle Peak Road. You can also catch the B1 to Lok Ma Chau (where you can walk the border over to Shenzhen.
The Yuen Long section of Castle Peak Road ends at the Sun Yuen Long Centre. This side of Castle Peak Road has some pretty awesome side streets where you can find some pretty awesome eats (i.e., Yau San Street!).
This side of Castle Peak Road also has a mini network of sky bridges that you can walk over to cross to the other side of the street and over the Light Rail tracks.
Above and below are a view of Castle Peak Road from the sky bridge. You can see the Light Rail track that runs straight through the middle of Castle Peak Road.
If not for shopping, walking along this main street is a great way to just view the town.