I pop on some Robert Johnson and sing really loud along to "If I Had Possession Over Judgement Day" before a gig. He sings so high, and I sing so low, that it really stretches out my vocal chords nicely. My first song is usually "32-20" also by Robert Johnson, which seems to really loosen up my voice and me (maybe more important). My usual gig is always very smokey, so I have to deal with that, and I usually sip Sprite during the night.