We never paid for anything OOP.
I traveled with my two kids (three of us total). We conserved credits by meal-sharing. The portions at Disney are HUGE and they have no problem at all providing extra plates (at both CS and TS restaurants). Obviously this rule does not apply to buffet meals.
A few of the meals were enough to feed all three of us (like the $13.99 chicken and ribs combo at Cosmic Rays in MK). At most places we ordered two meals and split them three ways. We weren't shorting ourselves in any way...we were always so full our bellies ached.
The credits we conserved were used to purchase breakfasts at the hotel CS. We drank from our refillable mugs with breakfast, and used the drink credits from the CS to purchase large bottled beverages such as OJ, powerade, etc...those drinks were brought to the parks or taken home with us at the end of the trip.
My total OOP cost for our entire stay at Disney was the cost of one refillable mug. We also bought some souveniers, but we did that at the cheap gift shops in Kissimmee on the last day of our trip.