When caught out like that, I tend to just make a coffee ( I have an espresso machine at home, so it's nearly all milk ), or just drink milk. Milk is a food and better for you than a diet shake. I find it fills me up just fine when I am not especially hungry and when I want more, I just make toast. If you've got kids, you're feeding them in the morning, just eat the same thing they do, that's what I do.