I'll tell you one very important thing I've learned (the hard way) about singing, and 'tiring out' my voice quickly; coffee. Stay away from it! It diminishes my range (low notes hae no power) and makes my voice strain very quickly. If I drink coffee within an hour or so of a performance, I will have to sing some songs a bit higher then normal (up a half step).

Also eating reduces my singing ability. I plan to eat my last meal no sooner then two hours before a performance, preferably more.

After that, I drink water ... lots and lots of water during the performance. I get and pee all night after the show, but it's worth it for my voice!