Grunt and package.json files for (in this example) packaging a theme for release. This should get you started -- plenty of Gruntjs resources out there.

Gruntfile.js

// This assumes you've already installed Node.js and any related dependencies.
// 1. Drop this and package.json into your theme root
// 2. Run: npm install
// 3. Run: grunt
// 4. ??????
// 5. Profit

module.exports = function ( grunt ) {

	grunt.initConfig( {
		pkg: grunt.file.readJSON( 'package.json' ),
		copy: {
			main: {
				src: [
					'**',
					// Files marked with ! will be excluded from the copied and zipped files.
					// !directoryname/** excludes the directory and everything in it.
					'!.git',
					'!.gitignore',
					'!node_modules/**',
					'!Gruntfile.js',
					'!package.json',
					'!release/**',
					'!my-theme.zip'
				],
				dest: 'release/'
			}
		},
		compress: {
			main: {
				options: {
					mode: 'zip',
					archive: './release.zip'
				},
				files: [{
					src: ['./release/**']
				}]
			}
		}
	} );

	// Load tasks
	grunt.loadNpmTasks( 'grunt-contrib-copy' );
	grunt.loadNpmTasks( 'grunt-contrib-compress' );

	// Default task.
	grunt.registerTask( 'default', ['copy:main', 'compress:main'] );
};

package.json

{
	"devDependencies": {
		"grunt": "~0.4.1",
	    "grunt-contrib-copy": "~0.4.1",
	    "grunt-contrib-compress": "~0.5.2"
	}
}