Yeah, it all depends if you are accompanied or not. Playing a song people know will help. Eruption might be a bit too much for a non-guitar audience but hey, I've never done a talent show, so no idea on tactics. If you can play sweet child well, then go for it. If not, simplify it a little so you can play it with your eyes closed...

I'm not american, but I quite often throw the first six notes of the star spangled banner into the start of the big old 'live ending':

waaaw waaw waaaaaw waaw waaaw waaaaaaaaaaaaaaaaw (crash of drums and big chord to finish)... ;)