I budget about $40 for myself and about $30 for each DS 7,9 for each day. That is only for food, treats and buying souvenirs. I usually don't have to pull out the cards to cover anything more than that.
My boys don't walk by something and yell and scream until they get it. At the start of the trip I give them each about $12 out of the $30/day as there spending money. It really makes them think twice about all the little purchases and once it's gone, it's gone. Last trip we were gone for 13 days so they each got around $160. They did budget quite well and each had close to $90 left to do with what they wanted when we got home.
My future little DISers told me to keep the left over cash to put it towards their next WDW trip flights.
I can't wait to take them and show them our new home away from home, AKV!!
They wondered where i was for those few hours but they'll have to wait for a year or so to find out.