You can buy the travel adaptors before you go, most electrical stores, bigger supermarkets, etc, sell them. Take at least two of them if you have a few things needing charged and your own chargers.
Be careful though, make sure that your uk chargers say "100-240v 50-60hz". Over there they use a 120v/60hz supply and that can cause havoc with equipment that is designed only for 230v/50hz supplies. If in doubt you can get one of these,
http://www.maplin.co.uk/module.aspx?...24488&doy=12m2 (ignore the "thing" you see straight away, there is a smaller version
http://www.maplin.co.uk/images/Full/up90x.jpg ) which will do the job. But every modern day charger should be able to plug straight in with no problems. Charging times may be extended, however, depending on how good the power pack is, many will obviously run at "half the power" as you only have half the voltage.