Glowstone wire

It's like redstone wire, but you place it down and it connects to a glowing block like wire. The glow for the wire is level 13, and will cut off instead of fading away like redstone; this wire may signal twice as far as redstone.

The glowstone wire also has redstone uses for block updates.

A trail of cheaply obtainable lining, may be obtainable by placing glowstone dust, or green variant of glow squid ink, or glowberries.

This is an easy way to find your way back through the huge caves as well.