I only cook for myself and my husband, no kids anymore, so I often add things like carrots, flax seeds, and squash to cakes, cookies, and also to bread when I make it in the bread machine.
Another things that I like is tomato jam. it sounds weird, but I make raspberry freezer jam, and add tomato that has been through the blender, and the little tomato seeds are just like raspberry seeds, and the raspberry jello adds the raspberry flavor, so even when I don't have some fresh berries to add, it still tastes delicious. it is also fine added to blueberry, strawberry,or blackberry freezer jam.