I used to fast before I had to go somewhere (long car ride, events where bathrooms would be few or none), in the theory of "nothing in -- nothing out"! But my doctor has told me that fasting actually makes colitis worse, and responds better to eating frequent small meals. Which is true, because I can guarantee flaring up when I skip meals.
Pepto Bismal helps me a lot, and it's perfectly safe to use on a daily basis. Just a swig or two a few times a day, and you will have more formed stools (but black in color) and also helps with urgency.