When traveling, there are many things that can possibly happen or go wrong that would require extra money to fix. While these things may not be directly related to the research travel one is doing, these expenses would not pop up if you weren't traveling.
For example, if one gets stuck in the airport on the way back to one's home institution, you may need to get an extra night at a hotel before you go home.
The question is the following: When is it appropriate to claim such an expense on one's grant?
There are clearly varying levels of such events. One is something out of your control like weather pushing your flight back a day. Some are completely in your control and you messed up, e.g., you miss your flight and need to pay a fee to get on a later flight. Others are due to scheduling conflicts and new plans arising, e.g., another talking engagement shows up and one needs to pay the flight change fee in order to make sure one can present at both conferences.
Are all/some of these scenarios appropriate for claiming against a grant or asking reimbursement for?