Here is what we put into them:
frozen berries from trader joes
one banana
frozen mango or papaya
almond milk
flax seed
fruit juice (whatever we have but trader joes makes an awesome banana orange juice)
whatever other fresh fruit we have
spinach (lots of it) or kale
I know some people add yogurt but since we are pretty much dairy free we use the almond milk. My kids INHALE these and I feel so much better about them getting their iron and vitamins this way:) Try one, you will be surprised!