I'm part of unless they need diapers you don't need to carry anything camp.
I have traveled to WDW with kids from two to adult and I quit carrying anything other than a small cross body bag once they were out of diapers. If I need something while in the parks, I can buy it. I've gone multiple times and this is just the point I'm at.
If it rains, they sell ponchos. I sometimes have ponchos in our suitcases and it if is obviously raining when we leave the hotel will go ahead and bring them.
If the kids are thirsty, they sell drinks. Once my kids were past the bottle stage they could drink out of a straw.
If the kids are hungry, they sell snacks. And what kid doesn't want Mickey head ice cream.
If the kid has explosive diarrhea (happened once during the diaper stage), they sell clothes.
If you start making a list you can end up with a huge bag ... common items would be ponchos, sunscreen, water bottles, snacks, band aids, Pepto, Motrin, large cameras, cell phone chargers (I just use a Morphi), change of clothes, sunglasses, hats, lip balm / chapstick.