Some ideas:

An Aerobie (like a Frisbee but goes farther and requires more skill)

A compass.

A Fisher Space pen.

An hourglass.

A chess set.

A nice shade hat for hiking.

A headlight/taillight set for a bicycle.

Balls for juggling.

A slide rule (if he's into math).

Northwest Passage by Kenneth Roberts (my dad read it as a boy, then I read it, then my son read it)

A harmonica.

A backgammon set.

A video drone (if you have a lot of money to spend -- I would have loved one of those as a kid)