Hi, I was just there this past December with a relative for an extended stay (10 days and enjoyed almost every minute) On average, we each spent about $50 per day. Some days we ate breakfast at Shoneys (about $5 to $7 per day, breakfast bar price goes up on weekend) and as we drove, we brought our own water, snacks and soft drinks (we had a refrig in our room) and ate breakfast in our room some days as we also brought cereal and purchased milk and juice there.
My budget sort of worked like this, $5-10 for breakfast, $10 for lunch (fries, burger and drink will cost anywhere from $7.50 to $10, pathetic) and up to $30 for dinner (this can vary depending on if you eat at one of the better sit down restaurants.
This past trip, I had scheduled a number of sit-down rest. for later lunches, ie. 2:00 p.m. (you get the same meal you would for dinner but at the lunch price), and ate better food. We got real sick of the fast food. However, we did have some late dinners at great rest. just for dining experience (LeCellier, Alfredo's, etc.) on average these dinners totaled abou $25-$35 per person (not including alcohol or desserts).
As for souvenirs, we did the majority of our shopping outside of the Disney property. There are plenty of shops that sell licensed Disney merchandise (esp. in Kissimmee on U.S. 192). We bought some light jackets (it was cold when we were there), disney t-shirts, disney hats, small stuffed animals for cars and a few other things and in total spent $125.00 for licensed merchandise. I bought two things while at the Kingdoms and I think they totaled about $35-$40.
Lastly my advice to you is to be conservative maybe the first 2 days your there, that way the last two you know exactly what you have and probably a pretty good idea how you want to spend it by then. Suppress the urge to buy (this can be very hard at times, trust me I wanted to wear so many of the diff. disney hats) and think what you will do with them when you get home.
Have a great time.