For an Sebastien - just walk downtown and find the first open bar. Try a Txakoli or Cider and a few food items off the bar - everything should be 1 euro. Then move to the next one, the next one and the next one. There are at least 20 to try. The best pinxtos is at the one hidden around the corner near the old church.
The Pinxtos bar scene is so great I never eat at a restaurant in San Sebastien - but if you do the high end restaurants include Arzak and Berasategui.
There is also a great restaurant in Getaria that serves fresh cuaght fish BBQ in the wall down near the dock.
Istagegi is a great cider house.