I anticipate spending cash each day on drinks. We are going to being breakfast from home (cereal bars, oatmeal, etc). But when you are in the parsk all day in the heat, you are always thirsty. I know that on these boards I have heard many ways to avoid having to buy drinks, like, places will give you a cup of ice free of charge and then you can fill up at water fountains.
As for souveniers - I always try to get an idea in my head before I go of what I can spend without putting myself in jeopardy once I get back! So I know I'll drop a lot of Christmas Ornaments and a few things here and there.
With a child - I'm sure it's a another story!
Good Luck!