I've never bought food within the stadium itself, so I can't really attest to the quality (other than the fact that virtually every football stadium in the world sells crap food) but what I can recommend is that you visit the SUPER AMARA (a supermarket) opposite the stadium at the Plaza Los Soldados and just stock up on some good food there. You're unlikely to have it removed from your bag, or you can just munch a few sandwiches before going inside. It's cheaper, healthier and avoids queueing at half-time!

There are some food options in the stadium, but don't expect the best cuisine in the world. San Sebastián is an expensive city, and inside the venue prices are even higher. If you are looking for a good place to eat before or after the game, go to La Venta de Curro. It's not traditional basque bar, but they offer a varied range of pintxos and it's a comfortable place to stay.