If you have a kid who loves cars and racing, a NASCAR birthday party is fun way to go. We did this themed party when my son was 3 years old.   It was easy  to put together (and we didn't spend a lot of money).

At my son's NASCAR themed birthday party we served "Nitro-Nacho". We started with a large bowl of corn chips/tortilla chips, a pot of chili and a variety of nacho toppings including some spicy salsa.  My son didn't want a cake so we made different sized chocolate chip cookies and served them with vanilla ice cream and  ice cream toppings.  

For party favor, I put my craft skills to the test.  I made binoculars out of toilet paper rolls. First I covered the rolls with fun craft paper and then glued them together and  attached a ribbon to both sides. I also made cardstock pit passes-- with real pit crew jobs written on them. We also gave the kids goodie bags filled with car stickers, a pencil and a couple matchbox-sized cars.

The games were kept simple-- to give the kids lots of time for lots of running around and free-play.  One of the stations was a paper license place craft.  The kids could decorate a fun personalized license plate.  Another station was a car racing track on our living room floor. The final station/activity was a cardboard box race.  The kids stepped inside open cardboard boxes and ran around our backyard "racing".  

Everyone seemed to have a good time, especially the boys (big and little ones). The homemade binoculars and the cardboard box races seemed to be the biggest hits of the evening.