gulpfile.js

var elixir     = require('laravel-elixir'),
    fs = require('fs'),
    assetsPath = './resources/assets/',
    bowerPath = assetsPath + 'bower/',
    cssPath = assetsPath + 'css/';

elixir(function(mix) {
    var cssLibraries = [
        bowerPath + 'bootstrap/dist/css/bootstrap.min.css',
        bowerPath + 'font-awesome/css/font-awesome.min.css',
        bowerPath + 'Ionicons/css/ionicons.min.css',
        bowerPath + 'AdminLTE/dist/css/AdminLTE.min.css',
        bowerPath + 'AdminLTE/dist/css/skins/skin-black-light.css',
        bowerPath + 'iCheck/skins/flat/blue.css',
        bowerPath + 'morris.js/morris.css',
        bowerPath + 'AdminLTE/plugins/jvectormap/jquery-jvectormap-1.2.2.css',
        bowerPath + 'bootstrap-datepicker/dist/css/bootstrap-datepicker3.min.css',
    ];
    fs.access(cssPath + '000-processed.css', function(err) {
        // if libraries are already combined I don't neet to do it again
        if (!err) {
            console.log('I will *NOT* combine pre-compiled CSS.');
            return;
        }
        console.log('I will combine pre-compiled CSS.');
        mix.combine(cssLibraries, cssPath + '000-processed.css');
    });
    mix.sass('**', cssPath + '001-sass.css');
});