You must hold your bag in a way that doesn’t highlight your shoulder shape. Backpack is not permissible to be worn by a woman as this not only discloses her shoulders but even her breasts as it makes the abayah real Tight!
Feet must be covered too as per the vast majority of the scholars. However, the feet’s shape can be shown as this can’t be concealed and are not as tempting as the rest of her body!