I've been on both sides of retail, grocery and merchandise (ex-Best Buy Merch, good luck to you Ernie)
Working the morning shift the day after Thanksgiving in merchandise can be hell, I imagine, but thankfully both years I worked there I started three hours before open and thus only had to work five hours into the day, I couldn't imagine managers and peeps who had to be that had to be there all day long.
In grocery, at least in my experience, the weekends after Thanksgiving were the lightest weekends I'd ever worked, since everyone was at the mall or elsewhere. Now the days leading up to Thanksgiving were another matter...