Sun> Not to sure about HK Disney, but I used to live almost literaly right next door the orginal Disneyland in Anaheim California. I dont know how many of these are applicable, but some thoughts:
1. If you can choose WHEN, I recomend going immedatly after one of the most popular times of year. For CA that case was January and Late Sept/Oct (after Xmas and Summer rush). If you can only choose the day, I recomend a tuesday or wednsday (both other days get alot of spill over from the weekend). Needless to say, avoid any holiday and any day immedately before or after. Finaly if there is a day where EVERYONE expects it to rain buckets, go. You will have the part to yourselves.
2. As soon as you get there RUN! The best time to get to any of the ride with lines is early in the morning. Try to be the first in the park, and the first on the rides. Leave things like shopping, eating, etc. later in the day. THis makes sense as well since you can do those with the AC, you can wait in line outside in the AC.
3. Food is pricey, however a couple of thoughts to keep things down. Packing a lunch is lame, however packing snacks/water/etc. is not. Unlike most parks I have been to, Disney will have some family resturant/less fast foodish type options. These are not only more relaxing, they are also a bit better of a value when amount and quality are considered. Finaly if you really want to take the time, leave the park. (Again I do not know what the HK set up is like) There is monorail that will take you to the Disney hotel, off the park, and they will give you stamp to get back in. There you can eat in the hotel (again a bit better than pricey fast food) or you can even leave and see what is in the local area (again I dont know what is around that area).
4. Shopping, one word DONT. Get customary embroidered cap, and then walk away. Give your husband/boyfried/stingy figure in your life the credit cards. Its all crap, obviously, and you can get cheaper souviners outside the park. Again to reinterate, think of the old hikers motto, leave only footprints, take ONLY photographs.
5. If you must get souviners for friends and family, look around the whole park. You can usualy find some funky things that will cost you less than the run of the mill mickey t-shirt. One of my favorite things as a kid was a pack of disney playing cards (Mickey the King, Minnie the Queen, Donald/goofy/pluto/somebody the Jacks, you get the idea) I got them for the price of normal playing cards at the Disney Hotel gift shop (again off site).
6. Wear sunscreen, carry water bottles. Everyone in the family!
7. It's impractical to carry a jacket for everyone or a umbrella, so get the largest cheap poncho you can find for the family to hide under if needed (small when folded, lightweight).