Hi Pinkie -
for my daughter's 2nd B-day I made smoothies for the kids in my blender - cut up fresh fruit, added ice and some type of liquid (some water and bit of apple juice or sugar free lemonade). Since it was in July, this was a huge hit on hot day and actually went far. I don't serve soda in our house - even to adults. Water bottles, ice tea & 100% juice boxes were in the coolers.
For food I made ziti (whole wheat pasta), small tray of sandwiches, a salad and grilled chicken breasts on the BBQ - extra rolls & condiments on the side for those wishing to make into a sandwich (bought by large wholesale quantity -like Costco). I felt this was cheap enough - not far from what it would have cost if did what 100's of others are doing: same old thing- rental place or pizza, hot dogs, burgers. Kids just get too much of that stuff. I also didn't rent an party item or entertainment - which saved money/put to healthy food choices (we have a pool & I made water games w/ balloons, buckets, etc). We certainly get helped by July weather for making backyard party.
We did have pretzels, tortilla chips w/ avocado dip, and veggies with dip for snacking too.
Good luck and have fun. The kids remember playing with each other most.