As you point out, under EU law, Regulation 261/2004/EC (“the Regulation”), you have rights where your flight is cancelled or delayed or you are denied boarding. However, the protection afforded by the Regulation is available only under certain defined conditions.
As an example from the European Commission EU Services in Ireland, under Air Travel, the word 'reasonable' appears dozens of times, most often in reference to the airlines obligations, but not when describing compensation. However, responses to several questions suggest that the passenger is expected to be reasonable, as well.
What if the airline does not provide assistance when the flight is delayed? Is the passenger entitled to claim reimbursement of any drinks and food and telephone calls from the airline?
The Regulation is silent on this. However, it would be contrary to the spirit and purpose of the Regulation for the airline to refuse to reimburse reasonable expenditure for items it should have provided under the Regulation. It is important to have regard to the word ”reasonable” here. Even if the airline does not observe it’s obligations in offering you the assistance it should under the Regulation, this does not mean that you should expect to be reimbursed for a five course dinner in the event of a three hour delay.
In a case ruled upon by the EU Court of Justice (31st January 2013, Denise McDonagh v Ryanair C-12/11), in addition to the facts, the Court was also asked to rule on the question whether the obligation to provide care has a time or money limit.
The Court of Justice responded that the EU Regulation does not provide for any limitation, either temporal or monetary, of the obligation to provide care to passengers whose flight is cancelled due to extraordinary circumstances.
This means that the air carrier is responsible for providing care to passengers for the entire period during which the passengers concerned await their re-routing.
If the air carrier fails to comply with its obligation to provide care to an air passenger, that passenger may only obtain reimbursement of the amounts which proved necessary, appropriate and reasonable to make up for the shortcomings of the air carrier.
In this case, the language of the Court was necessary, appropriate and reasonable. Mind you, the suit brought by a passenger whose flight was cancelled due to extraordinary circumstances, the closure of airspace following the eruption of the Eyjafjallajokull volcano. However, the Courts decision made it clear that reason should prevail, even in the absence of specifics.