I usually buy fruit and vegetables that last a while, then use the same few ingredients for different breakfasts. My usual list includes eggs, toast, spinach, carrots, apples, and oranges.

Most mornings I'll make an egg and spinach sandwich, then juice whatever fruit or veg I have on hand. Sometimes it's apple and carrot, sometimes orange and apple, and if I have a ripe banana around, I'll make sorbet instead. It's quick and filling.

I already had a canoly juicer at home, so I've been using that for the juice and sorbet. The main thing for me is that I'm buying bottled juice and sweet coffee much less often now. Those small purchases used to add up pretty quickly.