No matter how lightly you pack, you're bound to have to bring one bit of electrical equipment, either a charger for your camera, or mp3 player. Plugging it in around the world can be a bit of a challenge. There are two main issues..
There's good news and there's bad news. The good news is that most bits of kit have what voltage they run on stamped on them somewhere. You're looking for a sticker with "Volts: 230v" or some such. If you see something like "Volts: 100v-230v", you're onto a winner, it means that you can use that bit of kit anywhere in the world. If your bit of electrical kit has a separate power supply, such as your laptop, then you should check that for the "Volts". Now the bad news. If your kit as got a specified voltage like 230v it means you can only run it in countries that use that voltage. Trouble is how do you know which countries they are? It's unlikely that it will be marked on the socket in your hotel room, you'll have to check before you go. Most good guide books will state it somewhere, or use the link on the right to the IEC website which shows plugs and voltages.
There are voltage converters out there that will turn 110v into 230v, and vice versa, but they are usually pretty heavy so putting them in your rucksack might not be such a clever idea.
So you'll need an adaptor to convert your plug into something that will be accepted by the socket. N.B. an adaptor such as this is not a voltage converter.
There are lots of adaptors out there, but most will only convert one plug into one type of socket, that's okay if you're visiting one place. However not so great if you're a countrybagger, and you're bound to visit more than one country in a trip, and you don't want to carry a bag full of adaptors that take up valuable space in your bag.
One final bit of good news, there is one adapter I've found that will adapt virtually any plug into any socket, and what's more they supply an USB adaptor as well, so you can charge all your USB devices without having to drag a PC with you.
I use the PowerTraveller USB Travel Plug to charge my camera battery, iPod, and mobile phone (although not all at once!). It's more expensive than many adaptors, but I doubt if you'll never need to buy another one.