I would advise that you take enough to get you through the first day or two in euros then the rest in sterling travelers cheques, not euro cheques no matter what anyone says. This will give you a least protection on the cheques that if they are lost or stolen you can get replacements whereas if you take cash and the same thing happens you have lost it permanantly.Try to avoid changing your travelers cheque in the hotel if you can as you'l get a better exchange rate in Los Gigantes.
Try the restaurants in the small church squasre good food and not to expensive.