Can't say I've spent time at the beach in a really long time, but if I were to do so tomorrow, I wouldn't hesitate to bring one (or more) of the following knives that I own: yellow Mini Grip, Mini Pika, Rescue Stryker. My Presidio would probably do fine as well, or Resistor, for that matter. But the Rescue Stryker seems particularly resistant to rust, and the others should hold up just fine as well.
For 12 hours, it would be best if you could rinse the knives off periodically with non-salt water. With the BK1 coating, I wouldn't worry much about the Presidio (except maybe the Axis springs). Can't speak for the Chris Reeve, as I've never owned nor handled one.
As others have stated, a Spyderco Salt would be ideal. I do hope to own one myself one day. The only thing I don't like about them is the lock, but it should be worth it just for the steel alone.