I do quart-sized freezer ziplock-brand bags; generally, i don't get the plastic taste, but then i don't store stuff in them for a long period of time. The monthlong storage might be your issue, depending on how you store it. I lay out what i'm taking the day before i leave, pack it in the smaller bags, and go, avoiding heat as much as possible. I prefer the quart-sized ziplocks because i can adjust them in the bear can more easily.
A month or more wouldn't be good to me, unless frozen or kept really cool. My M&M's are kind of the keystone marker if the repackaged food get's too warm.