I sometimes add linseed to my oats too, for omega-3s and a bit of extra protein, etc. I buy 2 or 3 pounds of whole seed and grind about 2 weeks' worth every now and then, keeping both in the refrigerator. (As I understand it, flax seed keeps better if it's not ground, but intact seed doesn't get digested or absorbed well.)
I grind my linseed and keep it in a sealed container in the fridge.