After you've made up your list, total the cost of all your items, and add another ten percent to the price. If the budget comes out to be way over what you expected to spend, critically revise your list. Remember that people will eat more at your party than they do at a restaurant when they're paying for their meals. And here's the food list. Once at the supermarket, don't buy anything that's not on the list , unless it's something important that you forgot.
Impulse buys are the bane of a good budget.