Making alcohol out of them is a good option too :D
Mix with really strong black tea (for the tannin) and a bag of sugar - use a cider/champagne yeast if you want it uber dry or a low attenuating beer yeast (one that gets killed when there is too much alcohol) if you want it slightly sweet.
Just remember to sterilize everything really well (sterilizer solution used for babies is fine). That includes your hands and the tap nozzle.
RE: Doing more with blackberries