I'd hang my hat on:
* Gas tubes
* Transorbs
* Extremely High Power Zeners
* Massive High Voltage High Current Caps
All in parallel. That's the only way to have any hope of capturing the wide spectrum of an EMP. And even then, if a few components fail, you're hosed.
But here is the thing. Outside of certain MIL-STD and NEBS systems, very few electronic systems have anything more than low power zeners and standard off-the-shelf (easily cracking, easily broken down) ceramic caps. OOOOOOoooops!
Would make no difference. If your equipment is nto shielded you are toast. The traces themselves in a curcuit board will couple enough energy to blow semiconductors.