Agree with everyone else, it depends on what kind of souvenier shopping you are! We have gone once or more per year for the last 10 or so years and our kids are older, so we don't buy souveniers anymore. If we see some random thing we like, we get it but we usually don't.
You will need extra money for tipping, both mousekeeping and dining at Chef Mickey's. When we've gone with the dining plan, we have many snack credits leftover at the end of our trip so no extra money needed for snacks/drinks. Not for budget reasons, we just all have small appetites in our family.
If you tell us more about your spending/eating habits, we can all surely help you a bit morre.