Check with all your son's card providers to see exactly what charges will be levied on withdrawals abroad. Some are easily identified like a fixed amount per withdrawal or even a fixed percentage. In rare cases this may even be zero (cards offering this are few and far between these days, Even if charges are low, ask what exchange rates they are using on that day and compare with the wholesale bank rate - many providers will load this rate, typically by 2.75% (the "standard" VISA rate) or sometimes even more. If you are lucky you will get the wholesale rate. This exchange rate loading is generally hidden and can cost as much, if not more , than the explicit charges. Credit, as opposed to Debit cards will also charge interest, usually around 25% p.a. on cash withdrawals adding further to the cost (but still useful for accommodation, restaurants etc.)

Make sure you son notifies providers of when and where he will be travelling otherwise it is highly likely his cards will be declined.

Equestrian provides some excellent advice on safety which your som=n would be wise to follow. I would only add that in the , extremely unlikely event that he is robbed - just give up the money, the alternative is simply not worth it.

Prepaid cards area excellent alternative to credit or debit cards and have many advantages. They have been available in teh Uk for several years and are increasing in popularity. Usually much better fx rate and easier to replace if lost. http://www.fairfx.com/ has been around for some time and is a market leader here but not sure if they operate in the US yet. I think Travelex have a similar card. The modern day equivalent of travellers cheques.

Always sensible to carry two cards in case one fails and keep some cash in reserve, all in different places.