I think it depends whether or not you have neighbors who your kids know and could turn to in an emergency. Also, how far away are you going and how quickly could you get home if they needed you. I think 14 is definitely old enough to stay home alone, and I would also say that 11 is old enough as long as they have speedy access to a trusted adult (a nearby neighbor, or you on your cellphone if you’re less than 10 min away) in case they need something or hurt themselves.
For what it’s worth, I grew up in an apartment building in NYC in the 80s and my mom left us home alone when we were very young, as young as 4th grade, if she needed to run out to the store and get something ( but not for whole afternoons or evenings, just short trips). The difference was that we knew all of our neighbors in the apartment building and as soon as anything went wrong we had lots of grownups to turn to, so it didn’t really feel like being home alone was scary or dangerous.
Things are even easier now because in the age of cellphones, they can reach you if they need you, and you can check on them if you need them.
I would say, ask your 11 year old daughter. If she feels ready to be left home alone, you can certainly leave her for a short trip if you need to run out and buy something. Especially if her 14 year old brother is home too!