In the summer, most white Christians head for the beach in lieu of going to church. While combining the first and second services solves the problem of near empty sanctuaries, it doesn't much help with the huge declines in giving that coincide with drops in attendance. You might think that white Christians would tithe whether or not they skip a few services, but in reality, they tithe only in the weeks they actually attend church, as if they were paying for admission.
Enter the church yard sale. This event serves to get rid of all the old furniture and other unsolicited rubbish that has been graciously donated over the years. When this junk is combined with new crap specifically donated by the congregation for the yard sale, the profits can provide a modest boost to the church's bottom line.
Signs and newspaper advertisements will draw in hundreds of unchurched pack rats to the yard sale. Rumor has it that on occasion, a few of these heathen hoarders become so impressed with the junk on display that they immediately decide to join the church. So even if the gross receipts of the sale are hardly worth the man-hours invested, the opportunity for outreach makes it all worthwhile.
The church yard sale also allows white Christians to demonstrate stewardship by giving away items that are slightly too good for the garbage can. While one person's trash may be another person's treasure, in the case of church yard sales, one person's trash is that same person's treasure in heaven.