If you have chosen to rebook your flight due to being denied boarding and the air carrier fails to offer you reasonable care while waiting for your rebooked flight, you may purchase meals and refreshments (non-alcoholic) yourself and subsequently claim a refund for your purchases from the air carrier.
You may also get a refund for reasonable expenses for hotel accommodation and transport to/from the hotel if an overnight stay is necessitated by the rebooked flight.
If you have chosen not to be rebooked on another flight, you may be entitled to a full refund of the ticket price. You should, however, remember that you cannot have the ticket price refunded if you have chosen rebooking on another flight.
Remember to keep the receipts for your purchases so you can document your expenses to the air carrier.