Ultimately it is your choice on how you handle the finances abroad. However, there are three common options available to you when handling money whilst travelling. Your decision depends on how good your own personal security is and how well you do your homework on bank cards and conversion rates. It may be that you use all three of the options described below while travelling, and use a different one depending on where you are going and what you are doing.
Using a Credit or Debit card when travelling is perceived as the easiest way to handle your finances when travelling as you hand over the card, they swipe it, and the transaction is complete; but there are negatives associated with this payment method.
Firstly, especially in the less developed nations, many of the shops may not have card readers for direct money transfers and the market stalls certainly will not. If you do decide to pay by card anywhere, make sure that the card is swiped in front of you as you could be in danger of the merchant cloning your card out the back or swiping it twice. Always be vigilant. In some cases your card may not be accepted in the country. You would expect Visa, Mastercard, or Maestro to be accepted worldwide but this is simply not the case everywhere.
When using a card to get cash out of an ATM it can be advisable to withdraw larger amounts as infrequently as possible. This has the disadvantage of you having a lot of cash around and being vulnerable to theft, but it can also save you money as withdrawals from abroad can come with hefty transaction fees. It is up to you how you balance your cash withdrawals with transaction fees and the safety of your money. For free transactions abroad, look into Nationwide Debit Cards (UK residents only).
Despite transactions having high fees, you do get a very good currency conversion rate, much better than what you would get at a travel agents. This is because banks buy enormous amounts of currency at a time consequently lowering the cost of each unit converted, and giving you more foreign currency for your money. The same principle applies if you bought oranges wholesale; the more you buy the cheaper an individual orange becomes.
Relying completely on plastic is a bad idea because if you lose your card you have no access to your money. It is sensible to always keep cash with you in the occurrence of your cards being lost or stolen so you can support yourself until you can make other arrangements. Second to this cash is accepted by all merchants and vendors and is much more secure than having your card swiped because if you lose $10 cash, that will be the extent of the damage unlike with a card.
Many people say that the travellers cheque is no longer useful and plastic is the way forward, but travellers cheques are very safe. You buy, register the cheques from a bank, and sign them before you leave the country. You can then cash them in at foreign banks in exchange for cash or use them at restaurants or shops to pay the bill. When presenting the cheque as payment to a shop owner for example, the payee will countersign the cheque once convinced of your identity. They are a very secure method of payment because if the cheques are stolen from your bag, you can cancel them and get a refund or credited, something which is more troublesome to do with plastic and nigh on impossible with cash.
The down side of the cheques is that the banks will charge you a small fee on issue (usually 1% on purchase price and sometimes commission free), and another small fee is charged when you exchange the cheque for cash when abroad.
Try not to have too much money in your bank account at one time. I had a family member keeping an eye on my balance and ensuring my credit was between £300 and £0. This was to ensure that if a thief did get my card, the maximum they could take would only ever be £300. This technique only works if you do not have an overdraft. Remember, if your card is stolen, cancel it immediately or get a family member back home to do so.
Do not flash your cash. If making a purchase, sort out the notes out of site to avoid showing your wealth.