I think the deal with Ziploc is based on the fact that guests bring their own ziplocs into the park all of the time. Every "What to bring to Disney" list or tip or post or video seems to include Ziploc bags. So Disney's now going to hand one out to you instead.
I don't think them handing out Ziplocs erases the rest of what they're doing, especially if people get more than one use out of the bag (Which I figure they will if possible, if they are Disney branded.) I'd stick my camera in it, because that's what I do now with the Ziploc bags I bring from home.
And I'd use it again on any other water-based ride I went on. And if it was cute, I'd dry it off, and put some of my trip notes, trinkets, etc. in it when I headed home.
And in all fairness, I used to do the same with one or two of the plastic shopping bags, BUT, just 1 or 2. The rest I had no use for. So, now when I go to the park I'll happily drink without a straw, bring a small cloth bag with me for trinkets, and use soap that doesn't come in a tiny travel size bottle. And when I go on a water ride, I'll just have the option to use a Ziploc bag from WDW instead of one from home.