From the Football Ground Guide:
Various private car parks are available in the area around Ewood Park (especially along Branch Road), costing in the region of £5. If you want to get away reasonably quickly after the game (the roads immediately around Ewood Park are closed off for crowd safety for around 30 minutes after the game) then as you come down the hill on the A666, you will pass a BP Petrol Garage on your left. Turn right at the next traffic lights into Branch Road and down on your left there are some industrial units offering matchday parking. After the game turn left out of the car parks, so that you are going away from Ewood, turn right at the second mini roundabout and this will take you back up to the M65.
Behind the Bryan Douglas Darwen End, the Club have created a fanzone area, into which away fans are admitted. It has some large screens showing previous meetings between the two sides (great!!!) and more importantly food and drink outlets, where you can buy a 'Pie and a Pint' for £4.90.
Any other ideas?