Gift voucher for 14 year old boy?

[BewareOfTheToddler]

Am shopping for a 14 year old boy as part of the Met's Christmas present appeal. The suggested spend is £20. I've spent £10 so far buying a warm but very reduced beanie hat and gloves (it's freezing here today). What else could I get for £10 that a 14 year old boy might like? If a voucher, what for? Am wary of Amazon/iTunes as I don't know whether kids in these circumstances would be able to access them easily so needs to be a walk-in high street store.

Costa
Nandos
Game
WH Smith

I would get a voucher for New Look or somewhere...he'd be able to choose jeans or a top in the sale after Christmas if he wanted.

I wouldn't know what to get a 14 year old boy as I always just give cash to my nephews...obviously not appropriate in this case.

Good shout on WH Smith!

Some good ideas here, thank you! Game or Nandos would be great but we don't have them in my neck of the woods. How about H & M?

Thanks again - have gone for WH Smith in the end (would never have thought of that by myself!)