I wouldn’t worry too much about the DVD section. The first part is just clips and what is wrong in the clips it is basically common sense like a spilt bottle or wrong food label or something. The second part is maths most of which was very basic with only one relatively hard question.
After that someone will come in and speak to you. I got asked what I thought Sainsbury’s tried to do different so be prepared for something along those lines just saying it is one of Britains leading supermarkets and quality of products and customer service is what it focuses on delivering.