One of the things you can't fail to notice in HK is 7-11. I don't know how many stores they have here, but it seems like, on Hong Kong Island and in Kowloon and the New Territories, at least, you are never more than a few minutes walk away. There's one on Robinson Road a few minutes from my flat - which is one of at least 5 I can think of on or near the escalator - and at least 4 in Tsuen Wan town centre, not including the new one a block away from work.
They all, obviously, look very similar, and except for things like ice cream machines and food stations, they all essentially stock the same products. They all, as far as I know, can be used to pay bills and accept and top up Octopus cards - a common enough thing that a friend of mine was confused for a moment when he couldn't use his Octopus card in a 7-11 in Macau. They are mostly open 24/7 - though not all - and they're simply reliable - you know what you're going to get in any 7-11, anywhere in Hong Kong.
What you're going to get, however, isn't great. In the UK, convenience stores usually fall into one of two categories (sometimes both) - minimarts or garage (petrol/gas station) forecourt shops. Garage shops normally carry mostly junk/convenience food - prepackaged and dry and/or long-life - with the exception of things like sandwiches and milk, which you would expect to be delivered daily, and maybe some emergency dry groceries. Minimarts will normally have a more extensive fresh section, both in terms of fruits/veg and chilled, rather than frozen or vacuum-packed/pasteurised food. 7-11, unfortunately, is far more like a garage shop than a minimart.
The majority of the stock at any average 7-11 will consist mainly of sweets, fried snacks, drinks (including alcoholic), and fresh milk, sandwiches and other packaged food. Okay, I do look at the packaged food with a biased eye, since the majority of it isn't kosher and therefore isn't interesting to me, but still - it's obviously unhealthy convenience food rather than super/mini market type stuff. Again - I know that a lot of people in HK buy that sort of thing from wet markets rather than supermarkets, but there's no noticeable attempt made.
Don't get me wrong - I'm very impressed by 7-11 here. As I said, they're reliable, they're usually open and friendly through the night, they do non-retail things (bill pay, Octopus top-up), and unless you're on a small island, there's probably one a few minutes walk away. It would be nice if they sold slightly better food though...