I just said "be careful"
Here's Simon Calder's advice, which rojash may agree or disagree with:
Simon says: I am also off to Greece, and following political developments in Athens with interest — but not alarm. On Friday I bought euros for the trip, to lock in to the best exchange rate since 2008 (though it could improve still further in sterling’s favour). But because of all the uncertainty in Greece, I took two precautionary steps. The first was to add an extra €100 to my estimated spending; normally I rely on plastic for emergencies, but were Greece to leave the euro, electronic banking could freeze for up to a week and prevent debit and credit card transactions.
Next, I insisted on €5, €10 and €20 notes. The most likely form for a new currency is an overprinted “Greek” euro, whose value relative to the “real” euro would fall by perhaps 40 per cent. While traders sort themselves out, and before a market in the Greek currency begins, tourists are likely to pay in euros but be given change in new money. Pay for a €15 round of drinks with a €50 note, and you could get back change in Greek currency worth only €20. That is why low-denomination notes are so useful.
If Greece leaves before your trip? The euro is still the best currency. Moneychangers will spring up everywhere, offering keen rates, and you will be able to change euros to the new Greek currency in modest amounts as you go.