I didn't have any milk for the cereal one morning.
Previous times, I have used Orange Juice in it's place. It's not too bad.
Another time, I used water,which really brings out the flavours in the grains.
However, the best substitute that I have found so far, is a cup of COFFEE. I drink black coffee, no sugar, which probably would not be the choice of many.
Those of you who use "double-double" or "triple-triple," cream & sugar, in your coffee, especially, may not scoff so much.
Try it, you'll like it AND it may save you some time in the morning.
This helps out a few, "Lactose-intolerant," friends to enjoy cereal,, without expensive, milk substitutes.