For me, stuffing so much stuff in pockets makes it really uncomfortable for me and possibly having to search through so many different pockets may be time wasting in my book. Plus I am a bit paranoid about pick-pocketing. Although I think how much stuff you bring to the parks plays a role in determining whether to take a bag or not. If it's just a park map and whatever you have to hold your money with, then a bag may not be required. But if you're bringing more items like a camera, sunglasses, sunscreen, snacks, etc, then you'll need a bag of some sort.
"All my life I wonder how it feels to pass a day, not above them but part of them.
And out there living in the sun, give me one day out there, all I ask is one to hold forever. Out there where they all live unaware, what I'd give, what I'd dare, just to live one day out there."