A.B.
We had many of my children's birthday parties in the back yard and I'll tell you, they just play. We planned a few activities such as pin the tail on the donkey (or some version of that), a home made obstacle course, etc., but for the most part they just played. We had a bunch of beach balls (5+) we threw in the back yard and they played. We had healthy food such as fruit and veges, maybe a thing of chips and drinks such as water and juice boxes. We didn't need all the other activities and they had a great time running, playing tag, etc.
The 2 neatest goodie bags I have seen are 1. a can of silly string with a balloon tied to it and 2. a gift card ($2.00) for donuts.
I hope this helps. I have found kid's parties don't really require all the hoopla that adults think and the kids have a great time with all the unstructured play.
Good luck! A.