What can I use to film 2.5hrs of theatre?

Okay, I know this is awful of me, but... I've never done it before. There is a specific theatre event I *need* to film. It is a live production that is going to be aired in a movie theatre, so I will be trying to film it from there. I have no idea how many people will be in attendance, but....... I *really* just want to figure out what I could use that I could just rest on my knee or something (covering up the screen, of course, as not to bother anyone else around) so that I could get at least a decent version of the production on film for posterity (since it's a limited production and there will otherwise be no video of it)!

ANYways... I'd actually typically be the kind of person to roll my eyes at this type of a post, but... I have my reasons.

I guess the question is: what can I use to film this, preferably short of buying a camcorder. I have an iPhone 4S, but from what I've seen online, it'd take about 25G to film 2.5hrs and my iphone is 16G total (of which, about half is available). I also have a Panasonic Lumix, but the max for each individual movie is about 8min (and I don't want to just keep watching it and hitting record every 8min).

Ugh. ANY assistance in this matter would be GREATLY appreciated.

Thanks.