With my twins, I never pumped enough to really worry about freezing. They typically drank what I pumped one day at work on my next work-day. I don't think I pumped 500 oz total over 2 years of pumping, LOL! It was only with my 3rd child, when my body seemed to believe it still needed to make milk for 2 babies, that I had enough to worry about how to store it. It's important to remember that output with a pump doesn't reflect true production!
I used baby food jars. Since we don't feed baby food (and wouldn't have had jars available when I really needed them even if we did), I got them off Freecycle & from a coworker whose cat was eating the stuff. I didn't cap them tightly until the milk was frozen, just placed the cap over the top, then twisted the caps down later. I'd leave some space at the top - they only hold 2-4 oz anyhow, so not too much space. And they were the perfect size for storing breastmilk in small quantities. I don't know how well they actually sealed, but since I only worked part-time & only a small portion of my DD's diet was frozen milk, I wasn't too worried about the potential of nutrient loss. My 3-year old recently found some old jars in the back of the freezer (at least 1-2 years old, possibly older) and insisted on drinking them. They smelled fine & clearly tasted okay because she guzzled down a full cup in less than 5 minutes.
I do agree w/ PP, donating would be difficult if the milk was stored in glass, but not impossible & you may not have this issue.