See, there are many things that I love about Hong Kong - all that density makes up for a diverse…read morescenery, and all that commerce means everyone is at each other's throats for your business. If you are a savvy shopper, you pretty much know where to go for certain things. I know that if you want remote control cars or airsoft guns, you hit Kwong Wa street (廣華街) - if you want Legos, you hit In's Point (現時點). If you want a crap-ton of Japanese figurines, you hit Richmond Shopping Arcade (皆旺商場) or Sino Centre (信和中心). If you like diecast display planes, you hit West Main trading (西幹線玩具) near Prince Edwards MTR. If you want diecast buses, that's 80M bus shop, which has multiple locations in the territory. If you got the money you can try hitting the spiral at Langham Place (朗豪坊) if you want to check out the latest fashion accessories from Shinjuku or Seoul.
Me, I like collectibles - stuff like Rement food kits, F-Toys trade models, little double decker buses like the stuff that TinyHK (微影) put together. I enjoy collecting stuff like that for the display cabinet back in New York. Now, normally, you can hit Wonderland Superstores (奇趣天地) all over Hong Kong, but you could end up paying a lot, and their selection is often meh.
That brings us to Tai Yuen street (太原街). If you know your Hong Kong history, you would know that Lee Tung Street (利東街) used to be right next door - it's a 3 block long street of little print shops and stores that were the go-to spot for doing wedding invitations. The Urban Renewal Authority of Hong Kong (市建局) tore that entire street down and replaced it with a shopping mall, which gentrified the place but also killed a crapload of those little businesses. The URA is not known for being nice and understanding to the little shop owners, and none of them were invited back. Basically, Tai Yuen is a peek at what that area looked like in the past, and frankly, the place is a freaking jewel. Just wait until past noon if you want to see stuff bloom here.
First, check out the intersection with Johnson Road (where the Tramways run), the stalls in the middle sells all sorts of stuff like the Japanese fortune kitties. One of the stallkeepers there also has a really nice diorama of a Hong Kong Dai Pai Dong and a couple of buses, so thats cool. Then there's the toy stores. Well, there's really only, like 6, but if you have to choose one, check out Hung Hing Toys (鴻興玩具), which spans 2 storefronts and has nearly everything, from Gashopons, to Giant Robo figurines, to Legos, and to TinyHK/F-Toys/Rement figurines that I like so much. The others are still rather nice, but not as extensive as Hung Hing. You also got stalls with trinklets, bags, and stuff like that. Note that the usual crapload of cheap gaudy ugly Mainland products (ala Lady's night market) are kept to a minimum here.
Next, continue down the block - wanna try some snake soup? Se Wong Sun (蛇王燊) makes a decent meal out of them. Now, if you continue on down, you'll hit the market area on Cross Street - keep an eye out for a classically Hong Kong treat - Smith's Orange Jelly candy (史蜜夫鮮橙花軟糖), which is made by Smith's Candy company (史蜜夫糖果廠) out in the New Territories. It's the flavor that most Honkers grew up with, and there are usually at leas one candy peddler with bags of candies and a scale. They sell them by the pound, and you can mix and match. Smith's makes an Orange jelly, a Melon jelly, and the classic nougat. Keep an eye out for the produce markets nearby. If you want a real Hong Kong treat, hit Cross Street until you get to Spring Garden Lane, and then look for Kam Fung (41 Spring Garden Lane) - it's a decent with fresh out-the-door Bolo and Cocktail buns, and one of the best pre-blended iced milk tea in the Central district.
I hope you took photos, because this is probably as good as it can get in terms of outdoor markets. This is also about as good as Hong Kong can get.