This waterbottle (I think it's on woot or steepandcheap pretty regularly). It has a handle so it's super easy to carry. I put poop bags in the pocket. Then I take the leash and clip a collapsible water bowl to the end of it. Once we get to the off leash part, I just wrap the leash around my waist. I keep my phone in a pair of lululemon pants I found with a pocket. I put a chunk of dried lamb lung in the other pocket for treats.

Edit: I also SUPER don't trust any hands free leashes. No one else seems to agree, but having been dragged by a dog once is more than enough to make me never ever want to try it.