I had a jacket with side zips for venting and a crotch strap if you wanted when (push)bike riding which was lovely in northern england cold wet conditions, despite not being their heaviest weight material. It worked better with nothing on under it.
I also have a 4 season buffalo pile sleeping bag, which is two seperate (2 season?) bags each with a top, as opposed to a side, zip. The outer one has a pertex outer shell, a snug hood and zips each side to poke your arms out, which you then zip up again for toasty draft free coffee making in your tent. You could unzip the bottom to let your feet out, then you can wear your bag walking around arms and legs free, before bed
It is warm when damp, it doesn't care how dirty it is, it feels lovely on your skin, but is bulky and heavier than other bags and won't hardly compress. Mine is now 20years old, and not far off as warm as new.