Not football related, but things popular with my boy at that age (and upwards!):
Nice smelling but not expensive ‘aftershave’, the Police brand ones always went down well as the bottles are skull-shaped.
American sweets, eg Mike and Ikes, usually can get these in B&M.
Branded underwear (wouldn’t normally buy).
A boot buddy, for cleaning mud off, and boot bananas, for keeping the smell down!
One of the meter long boxes of Pringles.
Power bank.
Also, the year he was 12 I was so sick of being asked for various coloured pens, pencils and glue sticks as he was on his way out the door to school, that I bought a multi pack of black biros, a multipack of coloured biros, and a pack of 6 glue sticks, and wrapped them for Christmas, with the instruction to not ask me again until the summer holidays!