This weekend I took my DD backpack out for the first time. The drink holder is not at all accessible when wearing it... so it makes the whole thing a moot point! I had developed a habit of slinging the shoulder bad on my right shoulder, walking to my disc, and grabbing a drink. Using the backpack is a different experience! It's funny how we can fall into habits so quickly.
The point of trying to put the bag on my non-throwing shoulder is a good one. For me, it's just not comfortable. I may need to get over that to avoid using that shoulder, but I keep finding myself switching back without thinking. In bowling, I *never* pick up my ball with my throwing hand for that reason, but haven't translated that behavior to DG yet.