We celebrated our son's birthday at home with his meal of choice, decorated with our reusable birthday banner and Scrabble tiles and let the kids watch a couple episodes of Bear Grylls from a library DVD. He also chose which church service we were going to that morning. He seemed to enjoy making lots of the choices for the day and those things didn't cost us anything. For his gift from us he had asked for a cape. I made that for him from fabrics I had on hand and I made a personalized notebook that I modgepodged with cool paper and decorated with letter stickers for his name and washi tape.
In full disclosure, this no spend month (or at least 25 days worth) was prompted by an unfortunate amount of overspending. We had invited three of our son's friends to go mini golfing the day before his birthday, except that the weather did not cooperate at all. We had made a simple plan B for them to go to play at McDonald's and get ice cream if it started raining while they were playing. But by the time they picked up all the boys there was a downpour and lightning so they weren't going to play mini golf at all. So my husband had to decide on the fly what to do with the boys for a fun alternate activity and Itz seemed like the best available indoor option. Difference between what we were expecting to spend on mini golf and this option: $50. Ouch!
Lesson learned: Make a solid plan B for parties planned outdoors. Live and learn.