When abroad, you can not only lose money to a petty thief that single out tourists, you can also make unnecessary expenses (akin to losing money, in my book!) if you do not take care HOW you bring money with you during your trip.

If you have to withdraw from an ATM, make bigger (hence, fewer) withdrawals to cut the number of transaction fees charged by your bank.

When exchanging to foreign currencies, note that there is loss or gain in the exchange rates. When changing money in exchange bureaus (bureaux de change), make sure that you choose one that shows both their selling and buying rates. If you see both rates, you'd be able to see the bureaus corresponding profit margin which should be around 5%. Lack of transparency (only selling rate is posted) may mean that the profit margin is high.

Having checked the above, it would still also be best to still check and compare total cost of transaction since a good exchange rate are sometimes offset by high commission charges or no commission charge may mean a bad exchange rate.

As for cash... well, the only way to handle it well is to keep it safe. Get a money belt!