Gruntfile, with package.json. Handles sass, coffeescript, and image optimization. You should probably add .sass-cache and node_modules to .gitignore.

README.txt

1. Put these two files (Gruntfile.js and package.json) into your theme directory.
2. cd into the theme directory.
3. npm install
4. grunt

This assumes:
1. You have an app.scss file in assets/scss/app.scss, and that it compiles to assets/css/app.css
2. You have an app.coffee file in assets/coffee/app.coffee, and that it compiles to assets/js/app.js
3. You have images in assets/images - they will be optimized

Gruntfile.js

module.exports = function(grunt) {
	grunt.initConfig({
		pkg: grunt.file.readJSON('package.json'),
		watch: {
			sass: {
				files: ['assets/scss/**/*.{scss,sass}','assets/scss/_partials/**/*.{scss,sass}'],
				tasks: ['sass:dist']
			},
		  coffee: {
		    files: ['assets/coffee/*.coffee'],
		    tasks: 'coffee'
		  },
			livereload: {
				files: ['*.html', '*.php', 'assets/js/**/*.{js,json}', 'assets/css/*.css','assets/images/**/*.{png,jpg,jpeg,gif,webp,svg}'],
				options: {
					livereload: true
				}
			}
		},
		sass: {
			dist: {
				files: {
					'assets/css/app.css': 'assets/scss/app.scss'
				}
			}
		},
		coffee: {
			compile: {
				files: {
					'assets/js/app.js': 'assets/coffee/app.coffee'
				}
			}
		},
		imagemin: {
	    dynamic: {
        files: [{
          expand: true,
          cwd: 'assets/images',
          src: ['**/*.{png,jpg,gif}'],
          dest: 'assets/images'
        }]
	    }
		}
	});
	grunt.registerTask('default', ['sass:dist', 'coffee', 'imagemin', 'watch']);
	grunt.loadNpmTasks('grunt-contrib-sass');
  grunt.loadNpmTasks('grunt-contrib-coffee');
	grunt.loadNpmTasks('grunt-contrib-imagemin');
	grunt.loadNpmTasks('grunt-contrib-watch');
};

package.json

{
  "name": "Drupal",
  "version": "1.0.0",
  "devDependencies": {
    "grunt": "~0.4.1",
    "grunt-contrib-jshint": "~0.6.2",
    "grunt-contrib-uglify": "~0.2.2",
    "grunt-contrib-watch": "~0.5.1",
    "grunt-contrib-copy": "~0.4.1",
    "grunt-contrib-sass": "~0.5.1",
    "grunt-contrib-coffee": "~0.8.0",
    "grunt-contrib-imagemin": "~0.4.0"
  }
}