Obtaining any local currency other than one of the major ones such as US dollars or Euros before you depart for a country like India, Nepal or Chile, will require pre-arrangement with a bank, and it may not be possible at all (some countries don't allow their currency to be 'exported'). Do allow plenty of time (up to two weeks), particularly for more obscure currencies or if you are ordering from a smaller branch. The best bet is to purchase either cash dollars or travellers cheques and exchange them once you arrive. Most international airports have foreign exchange counters in the arrivals hall, and you should change at least enough here to pay for your taxi into town. Some small bills will be helpful. Avoid torn or damaged bank notes if you can.
Although officially offering foreign exchange, remote branches may be reluctant to serve you. So be prepared for transactions to take several hours. (Remember to take your passport along too).
You no longer need to walk the streets laden with large sums of hard currency at the start of your trip
The ease of obtaining local currency from ATMs in all but the most remote cities has made black-market transactions less appealing, and has the added benefit that you do not need to walk the streets laden with large sums of hard currency at the start of your trip. You are also guaranteed the official bank rate of exchange. If you have to exchange cash, look in a daily paper for the current rates. International class hotels will usually change money at their reception desks, but at poor exchange rates.
As a tourist anywhere you are very likely to be viewed as richer than the locals, and you may be a target for petty theft. Take sensible precautions and you are no more likely to be a victim of crime when on holiday than you are at home.
Try to familiarise yourself with the local coins and bank notes, and be aware of their worth so that you can give appropriate notes or coins - you won't be popular trying to pay for a cup of coffee or a bottle of water in some remote hillside village or from a street vendor with the equivalent of a £50 note (perhaps a month's pay locally) - and know what change to expect!
Don't flash your cash
Keep a small amount of currency to hand for things like shopping in the local market, taxi fares, or drinks from a local vendor. You lose points when you're bartering for product if you pull out a fist full of notes. So have a few notes in one pocket and 'reserve' money in other pockets.
Spread your cash around yourself and belongings. You are less likely to lose it all if a pickpocket does target you
When changing money, ask for small denomination notes, as they are always much more readily accepted than large sum notes.
Spread your cash around your self and your belongings. You are less likely to lose it all if a pickpocket does target you. Polythene coin bags (from a bank) can be used to protect notes from getting wet and are less bulky than a wallet or purse.
Be especially vigilant in crowded - or very secluded - areas.
Many garments made for travellers have 'security pockets' (pockets hidden behind others, usually secured with a zip or Velcro fastening) - use them.
Remember to check all of your pockets and hiding places for your money before you wash your clothes or pack your equipment away at the end of your trip!