Is it okay to leave a sleeping baby at home while you run out for a quick errand nearby?

No no. please dont, even if the baby is very young. To the adults, its a quick errand but to the babies, it is a world of time. What if a fire break out suddenly etc? A baby will be so helpless in such a situation and its definitely too late for regrets. For household consumables & groceries, either order them online to be entitled for free delivery or get them once a week on the weekends or after work if u are working. If really run out of food or ingredients to whip up a meal, ditch that & opt for meal delivery instead. At least u can have the piece of mind that your little one is safe and sound. They are too precious.