I've been in this situation in the past and am in it again right now - I find Hong Kong to be a really difficult place to manage weight!
Some tips that have worked for me (some of which have already been indicated):
1. Keep a list of EVERYTHING that you eat and also the calories in each item. If you put it in a spreadsheet, then you can easily add it up at the end of the day. You will be AMAZED at the willpower you get when you realise that if you eat "this" item, you will have to add it to the list and see the effect .... knowledge is power! By noting everything down you make a concious decision every time you eat, which tends to cut down on "boredom nibbles" that you eat without really thinking about it.....
2. To combat boredom nibbling again, like others have suggested, keep fruit and chewing gum (sugar free gum) in the office and snack on that instead.
3. Choose healthier meal choices and stuff that keeps you fuller, longer. Soup is apparently one of the best ways of staying full longer and at least is readily available here. Most of the other foods that are good (lean meat, vegetables etc) I find much harder to find for lunches in town.
4. Watch portion sizes. Usually they are too large - if you ask for a small portion, or stop the serving person when they try and add another spoonfull of rice etc, then you won't eat it. You can't eat what you don't purchase in the first place! (if you do this properly you should weigh portion sizes - obviously this is much easier at home, but about 80g of rice is right for someone trying to lose a little weight slowly and if you cook that at home then look at how big a pile it is, this will help when out).
5. IGNORE all the rediculous diet advice you get in womens magazines and most internet sites that are just trying to sell fad books. You lose weight by SLOWLY eating a little less calories than you burn and keeping it up for months and years. A "diet" is something that typically results in weight gain due to lower metabolism - a "healthly diet" is something you live on....
6. Exercise more. Do a mix of stuff - cardio workouts "things that make you puff" - good for fast burning of calories; resistance training "pushing/pulling/weights etc" builds up muscle and muscle burns more calories than fat and so increases the calorie burning while you are sitting still. Walk stairs when you would normally take escalator; walk a block or two when you would normally catch a bus; catch a bus instead of a taxi so you get the walk to/from bus stop etc etc.
7. Take a photo of yourself with nothing on. Keep doing this once per couple of weeks - and watch the difference. Measure waist and hip size; measure weight. Keep charts. These are all motivators and keep you going when you want to snack.....
Hope these help. They worked for me in the past and I'm getting back on the track again now. YOu have to find "coping strategies" for the things that trip you up.
For me, these are:
1. not enough time here to get to the gym
2. not enough access to healthy fast food
3. abundance everywhere of cheap, tasty fattening food.....!
So, you have to find you own ways of finding time for exercise, finding healthy foods and going out of your way to avoid the bad stuff.
Hope this helps.