I never noticed the 1st and 15th being a problem, our stores are always packed on Saturday afternoon and between 4 and 6 or so every night. Sometimes I think half the town goes shopping for supper every day. 
That wouldn't be so bad if most of them didn't either block the aisle totally by standing next to their cart while they spend 20 minutes looking at one shelf, or run across a friend and block the aisle visiting. Wal-mart should have traffic cops... 
As you said run across a friend visiting and blocking the aisles.
Unfortunately in today's life with membership down in the Churches we may only find a place to congrate is the local grocery store. Here we run into people we have not seen in 5 years. For the seniors that get out once a week if that to see a long time friend this is a wonderful meeting.
The stores are now the meeting ground for the young and old to meet and greet. Everyone has to go grocery shopping, sooner or later one will run into a long lost friend.
So what if others block the aisle, we can all ways go around them, I have no problem with kids running about, their parent may have sent them to find peanut butter or a can of beans. Crying kids tells me the kids are exhausted, hungry or uncomfortable, those cart seats would have me whimpering if I had to sit in one too long.
People that stand and stare at the shelves of products may be on a diet or have a medical issue where they must be very careful of the foods they eat.
So just go around these people and give them some room to be people other then your self. If one becomes upset that they cannot shop in peace, think about the others that want the same.
