I need to demo my games multiplayer without internet, can server help?

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I'm working on a game that currently uses photon for it's 1v1 matches. I frequently need to show a live demo for the game, but I'll occasionally get burned because I have to assume that the venue will have internet (or fast internet at cons). It would be a lot easier and safer if I could just bring a 3rd comp to work as a local server.
I don't know anything about servers really.
Can I use server like this?
Would it be plug and play, or will I need to be changing parts of the game, and doing stuff to setup the server?
Is there a license I can use that would be free (and preferably would never need to be updated)?
Since the comp would be mobile, is powering it on gonna be an issue? Or could I get it to start everything automatically?

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