You can't always get what you want, or what you need
While there’s plenty of awesome food to eat on your trip to East Asia, and grocery shopping there is a great learning activity as well as fun, there are some things that you just can’t get, even in Japan or Hong Kong -- or won’t be the same as what you have at home. Also, you may have your own dietary needs (hypoglycemia, diabetes, etc.) that don’t necessarily conform to a tour guide's itinerary, or your own jet lag.
And if your child is young enough to be taking formula, you’ll want to bring some of that along for certain, as Western brands have tight supply throughout the region due to the ongoing safety issues with Chinese-manufactured formula.
Items we had a hard time finding (or finding at a reasonable price) included:
Graham crackers & saltine crackers
Granola bars / fruit bars
Oatmeal / Cream of Wheat
Mac ‘n Cheese - the kind you only need hot water for (in-room microwave access may vary, if not available there's usually a hot-water kettle setup.)
You’ll probably be able to get your fill of fruit at mealtime, but little snacks of raisins, Craisins, cashews, almonds are a good idea to carry.
Finally, one category of must-bring items from your kitchen includes:
Ziploc bags of various sizes
Ziploc / Glad / Rubbermaid plastic bowls with lids
Don’t assume you’ll be able to pop into a McDonald’s and grab a plastic spork from a container next to the napkins -- it’s an unnecessary expense to them in cultures that do not routinely use flatware.