From the park, the nearest parts place that would most likely be able to get you back in service is apx. 20 miles away.
That being said, a small stash of U-joins, bulk brake line, belts and hoses wouldn't be a bad thing to have handy.
If you break it beyond that, you're most likely looking at being done for the day anyway.
They're just trying to make it a little more convenient for the guests, and possibly save them a couple of hours on a repair/travel time.
That way the guests can spend more time out on the landscape breaking the serious stuff!