If your flight is delayed for a long time then your air carrier must take care of you. They should provide you with meals and refreshments, access to a telephone, computer or fax, hotel accommodation where necessary and transport between the airport and the hotel.
If the air carrier fails to provide this care and you are forced to make your own reasonable arrangements, then you should keep all your receipts. You should then submit copies of these receipts to your air carrier as soon as possible thereafter (some air carriers request original receipts in which case you should keep copies for your own records).