I'm assuming you're from Carleton in Lancashire?
When coming to Barbados take USD and GBP from the UK. Don't purchase BBD in the UK as you can receive a much better rate in Barbados. If you purchase BBD in the UK the rate won't be nearly as generous and is currently around £1 to $2.88. In Barbados, you'll get about $3.06 currently for £1. You can do the exchange at any of the several commercial banks on the island including CIBC First Caribbean International Bank, Barbados National Bank, Butterfield Bank, Scotiabank or the Royal Bank of Canada. They all have the same rates as set out by the Central Bank of Barbados.
I would recommend you get your USD from M&S Travel Money which is commission free with very competitive rates. Normally you get about $1.50 USD for £1. USD can be exchanged on the street in Barbados at $2 for $1 USD. However, in some stores/restaurants, you will receive anything betweeen $1.95 and $1.98. Anywhere around $150 to $200 USD in small bills ($5s, $10s and $20s) should suffice to get you started and for tipping.
Also take your credit/debit cards.
Hope this helps
Edited: 8:59 am, January 26, 2012