I use an iPad for all my gigs because it is more portable and quicker to power up than my MacBook. I've got a 128gb IPad Air 2 and it has plenty of storage space for the 10,000 or so songs I'm most likely to need.

I use a Reloop Beatpad as my main controller and have just bought a Reloop Mixtour to replace an MC6000Mk2 as my back-up controller. The app to use is DJay Pro which I consider to be every bit as good as Serato, Traktor and Virtual DJ (all of which I own). Without getting into the legal ramifications of using it, the integrated Spotify functionality can be a godsend for obscure song requests. Oh, and it only costs about £10 for the app so is a considerably cheaper option than the others.