Good advice above. On the stage to acclimate for tuning, but leave it in the case for a good while if there is a severe temperature change to deal with.

Gig equipment disaster stories?...

Not one that happened to me personally, but one a friend told me about: Seems he was playing a dance where the band was on the floor mwith the crowd. The guitarist- lead vocalist of the group had recently acquired a new Gibson Jumbo and it was his first gig out with it. Of course the requisite drunk had to take up a position in front of him and after a favourite song of his was finished, the drunk leaned forward to offer his conspiratorial encouragement and accidentally dumped pretty much a whole glass of beer straight into the soundhole of the player's new Gibson.

The player felt slightly bad much later for cold-cocking the drunk.