What to Expect When You're Expecting Didn't Let Me Know

Lil' dude is three-and-a-half months old. We're getting pretty good with the everyday routines by now. The Dad wakes her each morning to feed her, I get her ready in her miniature duds, and he takes her to daycare. At night I bathe her, read stories, rock, and tuck her in while her noise machine spits out bumbling-brook sounds. Neither the Dad nor I have any questions about these routines. When we take walks with the dog, he holds the leash while I navigate the stroller through the March slush or strap her onto my chest in her carrier. I know which stores her carseat snaps into the carts best, and which stores are better to use the stroller in. But, there is still something I can honestly say, "I don't know" to. I am wondering if anyone will tell me so I don't have to be embarrassed to ask.
What is society's stance on leaving a baby in a car while adults runs into someplace very quickly?
I mean, do you have to unstrap the snoozing infant from the warm confines of her comfy carseat wonderland, while waking her with the jostling, to bring her into the cold, wet, very windy atmosphere outside the car while you return one disk to Redbox, or drop of the bundt cake you baked for a funeral at your church? I, of course, being the rookie mama I am, still do just that. Unstrap, jostle, awaken, and drag into the cold while I do these 10-second errands because I am unsure an alarm will sound if I were to leave the lil' dude in the back of the vehicle, alerting the Authorities to my heinous crime.
For example: last weekend. I took the lil' dude to the grocery store with me while the Dad stayed home to take the Christmas lights off the house (yes, we are Those People). I knew which grocery store's carts snap her carseat into place best, of course. She snoozed pretty much the whole 30-minute ordeal. I must soothe her to sleep when I talk out loud to myself while shopping. Anyways, upon checkout, my cell phone rings. It's the Dad. I thought he was calling from the backyard to say he was laying in a mangled heap after falling off the roof. Instead, he asks if I could go to the liquor store to look for the New Beer he's been wanting to try. I tell him sure. So, I wheeled the lil' dude, still attached to the cart, and all my paid-for groceries through the store, through the deli, through the attached convenience store, to the outside, down the narrow sidewalk, and into the liquor store. Babies in liquor stores is a separate topic for another post. No New Beer. So, I retrace my steps, and get out to the car, and load the baby up. On the way home, I think of the two other liquor stores along my route, so stop at the first one, wrangle the lil' dude out. In we go, and out we come sans New Beer. At the third liquor store, I stay in my car after I park, and look in the backseat at the babe, dozing again and think, "Can I leave her, with the car running, lock the doors and run in for 45 seconds?" It's broad daylight, I am at a liquor store in my tiny town. I think I know better. Out comes the little dude, and in we go. Nope. No New Beer here, either. We go home.
So the next time I traipse all over 2 counties looking for elusive things, like, New Beer, is the lil' dude supposed to accompany me each time?