Oh God, pleeeeeease don't do Elvis' diet!!
3lb is relatively easy so long as you do what Dot<B/> says and (part) of what stuel advises.
Set yourself the full week to achieve it. Then plan your meals ahead and eat healthy dinners of grilled fish with salad, followed by fruit. Have cereal and fruit for breakfast and salads for lunch (ensure your salads are varied to include fish, egg, potatoes etc.). Cut out crisps, chocolate, cheese etc. for one week and drink only water, green tea, fruit tea or fresh juice.
And if you fall off the wagon don't lose hope! Just get straight back on it again. It's only 1 week after all. It'll fly by.