Consignment and Resale Software
The very best option for seasonal sales is Best Consignment Shop Software. It's a one price (by the person who purchases the software). Purchase includes a 30-minute demo to assure that the program does all that is required and works properly for the intended purposes. There is no 'annual support plan' but support is available if needed at rates about half that of local IT services.
Consignment
The cheapest way to stock the shelves and racks at a seasonal sale is taking inventory on consignment. In Best Consignment Shop Software items can be marked down as the sale progresses to encourage purchase. At the end of the sale, unsold merchandise can be returned to consignors, donated to charity, transferred to shop ownership or destroyed.
The program allows variable consignor percentages so friends and family might get more of the sales proceeds than other sale participants.
At the sale one computer would host the program and inventory and POS (checkout) stations would connect to the host to share the same data in real time. Sales records will be invaluable so it would be prudent to backup the data frequently during the sale to preserve records.