1. Consult coolrunning.com for running races in your area (or whatever website you use, coolrunning in the most comprehensive for USA).
2. Drive to parking area for start of race (or walk or ride your bike if its close by) at least half hour before the start time. Just go to the starting line and run without a number. You can just say you were going for a run and noticed other runners so you decided to join in. They can't legally force you not to run. You just wont have an official time or another t-shirt which you dont really need.
3. Finish run. Then usually there's refreshments at the end. Consume your individual portion of fruit. Wait til most of the people have come through for their fruit. Then ask if they have any of whatever fruit there is left that they don't want/help consuming etc. I did this today and I ended up with 3 big freezer bag fulls of oranges that they didnt want. I ate two of them and put one in the fridge for tomorrow. Simple. :)
It's crazy only a few people would take 1 freezer bag full that I got three. I thanked the volunteer. I wish I had my car cause I would have put the oranges in my car and offered to help clean up in return for the goods.