Ballet flats are not suitable for Y7 girls, IMO, as their feet have not stopped growing, and the shoes stay on by being too small for the foot. (Speak to a podiatrist about it.)
DD2 wore lace up "jazz shoe" style shoes last year (Y7) and they were a PITA, because she didn't want to take the necessary time to loosen the laces, then do them up, so she walked down the backs. The soles also wore out before a full year (Clarks shoes). She now has black Kickers.
DD1 goes to a different school where being nerdy is okay, so there is less of a issue about what shoes they wear. She wears Mary jane type shoes, and so do many of her friends. She is going into Y10.
Re bags, I bought them both Cambridge Satchell Company "Batchells". The biggest size. They were expensive, but they will have them for years. At DD1's more fashion conscious school, lots of girls are very admiring of it.