Slava Vakarchuk, singer for Ukrainian rock band Okean Elzy, treasures his vintage 1969 Martin acoustic guitar as his most cherished piece of gear. He describes the instrument as something he can't live without, particularly while performing on the frontlines in Ukraine. It helps him boost the morale of the troops, whose writings and signatures now cover the guitar's face.

"I don't even want to call it equipment or gear. I would call it my friend — my musical friend," Vakarchuk says. For more episodes of It Goes To 11, visit GRAMMY.com/videos