You get a refillable mug with the DXDDP, are you filling it up in the morning at your resort and take it with you for the day? I am aware that I cannot get a refill in the parks, but thought I can buy bottles and fill it in myself or just fill up my mug with just water (and can I ask for water everywhere?). Is it worth using snack credits for soft drinks?
Who in their right mind would want to nick someone's used mug?! How annoying!
I've heard Disney coffee isn't that great, but do like ice water better than bottled water. Hmmmm...decisions, decisions...

Of course, this only works if you have your own car. If you don't, carry a small ice chest in your stroller. This works well too!