Talk

Take £100 odd in euros and withdraw the rest as needed with your normal attention to budget. Put money on a prepay too, always have a backup.

Remember to tell bank you are abroad.

Assume UK prices for eating out, hope for a nice surprise! Excursion prices should be available on line but it does depend what you are doing.

I would take a couple of hundred Euros and then withdraw any extra you need when you're there.
Meals out cost similar to the UK, but portions are larger. Be aware that many places in Greece prefer cash and don't have debit/credit card facilities, so I would check that there's an ATM near where you're staying.

The hotel will have a safe to keep your card/cash/passport secure.

Thanks for the advice. Bought £160 worth of Euros today!