I just came from a Maine vacation. Trying to return bottles to a grocery store were I bought them and get the deposit back proved impossible.

You would have to register with a company named clynk. (I think you need their mobile app as well.) They provide an initial free batch of bags which you fill with you bottles, then drop off in a designated container and eventually the money will be credited to your clynk account. Once you have used up your bags you have to buy new ones.