All three of my children go shopping with me everytime.
I find that having someone "babysit" my children while I'm doing something that needs to be done for the family isn't a luxury. I find it not something that fits our parenting style.
I enjoy that I can take 3 children to the store and shop either 15min or 3 hours and they are still very well mannered and very well behaved. I'm a prepared mother as well. My children have tasks and they have a little bag of fun things they're able to do when mama is rushing around getting this or that. 90% of the time my children are very involved in our family outings, such as going to the P.O., grocery store, running simple errands. To us this is how our children will learn to be respectful and have manners. They enjoy going too. On occasion they ask if mama can go with the other kids and they stay with daddy and they are welcomed to that as long as my dh doesn't want to come shopping too.
I have a lovely sister whom isn't one to take her children to the grocery store, otherwise she'd come up spending no money, getting no groceries and be a frazzled crying mess. Simply because she's never trained her children up. However I support her as I love her and she's my sister and it's her parenting style so I happily watch her children so she can shop.
I go prepared each time we leave the house, whether it's down the block or out of town. Snacks, Books, Coloring Activities, Favorite Toys all in their own backpacks. They are also welcomed to pack a snack bag or lunch which they enjoy doing the most as they get to put in apple slices, sandwich and carrot sticks just for themselves. While I'm getting the baby together they color their brown sack lunch sacks or if they choose to take cloth sacks they help mama get waters and blankets.
My 4yr old and 6yr old know what brands we get, how much of what we get and where we get it everytime. So shopping with them now is far more helpful than when we first started going. We shop Aldi's and as long as no one else is in the store and I'm in the aisle with them they are happily shopping for what we need as I say on the list and bring it to the cart with a glow in their eye and a smile across their face, so proud to help!