I agree with others that a 5th year of university is something that we as parents should prepare for. Some common reasons are a late change in major or a double major. In difficult majors it might also be needed to take 4 courses at once rather than 5. Kids can get sick in the middle of a semester or have a bad breakup just before finals. One good thing about an in-state public school is that you will probably still be in-state for the 5th year.
We had our septic system fail while both daughters were in university, and also had one car start to fall apart (major oil use after 175,000 miles) and needed to replace it. Of course pretty much anything can go wrong with the house or with careers or with the stock market.
One daughter needed a car to get to a major-related off campus job. The other needed a car to get to a research internship. Both were academically very valuable and for us worth the cost of a car (used, but not too old).
A loss of merit scholarship due to not keeping grades high enough is another possibility. Fortunately we have not run into this one.