What I carry varies based on where I'm going and how long I'll be gone. I re-pack the bag quite often, just to check on things and makes sure nothing weird is lurking at the bottom of the bag. (Like what? I dunno. A rubber worm? A stretchy caterpillar? I never know!)
A quick trip to the store, it's usually one clean diaper, my wipes, barrier cream and whatever sensory stuff I feel like taking.
For a day out, I'll pack in two or three clean diapers, my wipes, barrier cream, and a pair of shorts/pants/socks. (I can, as gross as it is, deal with a yucky shoe long enough to get to the car. But then it's coming off and the clean socks are going on. Blegh! PEE SHOES!) I've never had to change my pants, but there's always a first time for everything!
I made the mistake of not taking the bag when we went to the store. I ended up having to buy wipes and pull-on diapers because I had an incident and there I was. After that, I've always made certain to take my stuff. Why settle for something that isn't going to work very well when I have 'the good stuff' at home?
(I call my issues with peeing myself 'incidents' instead of 'accidents'. XD It's an incidence of pee in the pants. Inside my crazy brain an accident implies that some sort of outside force did it, like a giant smooshing my bladder until it pees. :laugh
I don't carry ziplock bags or wet bags because I generally have a bathroom available and the trash cans are big enough. If not, I suppose I'll just shove it back into the bag until I find somewhere to toss it out.
(Although I may carry a wet bag for "just in case" pants changes...that would be a good place to put the wet things and not make my bag smell.
)
ALSO: I have a vast array of bags. I have smaller 'over the shoulder' satchels for short trips and big backpacks for longer days out.