Given that the hackaton might be 2 days, unless your idea is 'simple' enough to have a MVP in 1 day (never seen it happen), the second day will be all preparation for the presentation because this is what will win a jury.
While we where working on our latest startup (omnipasteapp.com) we needed a way to get reports on application crushes from our early adopter. Existing solutions where either to expensive for a startup or did not had support for all the platforms we needed.
So we created bugfreak used a couple of weeks and then opensourced it: