The first rule of travel has always been to carry enough currency. While trekkers rolled them into socks, backpackers carried traveller’s cheques that were worthless if there was no merchant handy. Corporate travellers used debit or credit cards but were saddled with a 1.5-3% conversion charge while exchanging money as per the rate of the day. And then banks came up with the idea of pre-paid foreign currency cards. But these were single-currency cards, inconvenient for globe-trotters.