Have found several Wal-Marts that have refused when I ask to stay a few hours. Then my next question is where is the earest church?
Stay as long as you leave the lot cleaner than you found it, Next morning go in the church and donate $10-$20.00 they will apprecite it and stay our of Wal-Mart for groceries and fuel.
Normaly this is not Wal-Marts doing its the local campground operator that has petetioned the local government to stay out of Wal-Mart and into their campground. I have not found a church that will ask you to leave nor will the police ask you to leave a church parking lot.