I haven't tried that before. But, I just think if U can find a nursing room (with tap to wash hands)and squeeze milk into a cup with lid (maybe add the cereals first before squeezing)
I haven't tried it yet, but I am thinking may be you can pump out some breast milk (just enough for mixing the cereal) and put it in a small bottle, like a Pigeon 4 oz bottle, and put it in a cooler bag when you go out. Heat it up by putting it in a bowl/cup filled with hot water when you need to feed the cereal and then mix the cereal and feed your B. I plan to do this when I need to take Katrina out for longer time, although now, I am like BB618, I will prefer to feed Katrina the solid meal at home.