Unexpected Extra Travel Costs and Grants
These things happen, and as long as the expenses are reasonable, they should be covered by any reasonable funding body. It is a good idea to make a phone call to see whether you are permitted to spend the money, or at least to find out what budget limitations you have.

For instance, the other day my plane was diverted to a different airport. The only way I could make the PhD defence on time was using a taxi. So I took the 80 km trip and paid the 230 euro and fully expect that I'll get this money back. 

If I had have purchased a used car to get me to the defence and a bottle of whisky for pain and suffering, I wouldn't expect to get that money back.