One way to keep your berries fresh longer is to prevent molding. The key to preventing moldy berries is vinegar.
Prepare a mixture of one part vinegar (white or apple cider work best) and ten parts water.
Dump the berries into the mixture and swirl them. Drain, rinse if you like (the mixture is so diluted you can't taste the vinegar) and put in the fridge.
The vinegar kills any mold spores and other bacteria that might be on the surface of the fruit.
Raspberries will last a week and strawberries almost two weeks, without getting moldy and soft.