In response to a hack suggesting disposable changing pads as car seat poop-protectors, @Heatherikki pointed out a smart non-disposable solution: the washable Piddle Pad, made specifically for this purpose!
At under $12, it would pay for itself pretty quickly given how many disposable changing pads one's kid could go through.
Useful for the diaper blowout stage, and again during potty training. The Amazon reviews are excellent with folks saying it washes and holds up well.
I sure wish this were around when my son was a baby.
More: Potty training hacks