I also buy boxes of doggie poop trash bags from the Dollar Tree. They are 75 bags/$1 and are the perfect size for containing a stinky diaper or wet outfit.

Sigh! Sounds like us, but add 2 coolers with special food and drinks. My daughter is 4 and 75% of her clean clothes live in the minivan because she often has blowouts when traveling in a car seat or stroller. I use a small backpack with 3 gallon ziplocks: one has 3 outfits, one has 8 diapers, one has wipes, and on top is a receiving blanket (to lay down on for diaper changes). In the little front pocket are emergency snacks, stickers, a small toy, and chewy bracelets. In the car is a Tupperware box with clean diapers and a ziplock bag with wipes and a receiving blanket. I keep another large school backpack in the car with 3-4 outfits, extra receiving blankets and socks. I refill the little one from the big one as needed.

Sounds like you are a well-prepared and organized mom. I had kids 3 in diapers for some years and my life was all about poop and diapering (and taxi driving 2 ASD kids around for therapies) Now I have no children in diapers. This too shall pass. But now you are in this phase, I send you thumbs up and love.