“Going to the store for a gallon of milk” can be easily done with my largest handguns, except for the Daniel Defense DDM4V7P. If/When I am too lazy to gear-up with a holster, it is actually quickest and easiest to tuck a medium/large revolver into my waistband. There are two places, on each side of my anatomy, where a large revolver will be quite stable, if I am wearing a belt, and even my bicycling shorts have belt loops.
I do not own a .22 derringer, or an LCP. They are so small, I would have to hold them “just so,” in my long hands, with my trigger finger held in an uncomfortable way, and I hate having to do that. I do have a Seecamp LWS-32, with an adult-length length of pull, but it is heavy enough that I have to wear a belt, to keep my trousers in place, if I have that substantial assembly of stainless steel in a pocket. So, yeah, a big revolver is my lazy-moment gun.
When I do pockert-carry, is is with preparation, and intention, so not normally a milk-run thing.
I will assert that convenience stores and grocery stores are hot spots for crime, so not really the best place to be casual about anything.