Someone told me to bring a themal cup (e.g. tiger brand) and some rice. In the hotel, use the coffee/tea kettle to boil the rice for a few minutes then pour the whole lot into the themal cup, and after few hours it should become congee. May be you can try this at home first to see how much rice/water needed and how long it will turn into congee. But I'm not sure about the meat/vegetable. Guess you can bring some baby food and add to the congee afterward.
this method suggested by danielle is quit ok (I do this every night before I go to bed & then boil the 'congee' the next morning again) but of course not as good as you boil the rice la.