Hello! I know loads of people are collecting the backpack, these codes worked for me and I have enough for the backpack now, yay;
FACEBOOKPC
WMPROMO
TESCOPROMO
ASDAPROMO
COOPROMO
JSPROMO
NEWSLETTER (not used, don't know if it works)
Mothersday (used earlier this week, not sure if it works now)
Hope they help someone!