The Linux distribution Tails will automatically wipe RAM when shut down, which can be triggered by removing the USB drive it is running off of. I guess the thing to do would be to only work in a place where you can delay law enforcement long enough for the wipe to complete. But alas, it seems Ulbricht wasn't paranoid enough.

https://tails.boum.org/doc/advanced_topics/cold_boot_attacks...

Or, of course, thermite always works.