Backup laptop

How are people managing backup laptops with rekordbox? Over in the serato side of things, it was easy to take two laptops to gig (one with a backup of Serato with a mirrored library). Esp for the mobile DJs doing things like weddings, how do you get by with a backup?

I am happy to buy a smaller DDJ unit (in case my DDJ-RZ fails) or keep some extra powered speakers, a few extra XLR cables, but the thing that I can't make a backup of is my Macbook pro.  I would love to have a second copy of Rekordbox installed on a lesser-spec'd laptop in case disaster strikes and my primary laptop doesn't boot or has some other failure.  

I wish Rekordbox authenticated itself via hardware so when it detects a DDJ-* unit it unlocks the software (or a DJM-900, etc).  Alternatively, i would be happy with a couple of one time use licenses (that do not need internet) to use for 24-hours in order to get through the gig.

Using a trial copy is not an option because when I load the software to set up my preferences the timer would start ticking.

Thanks