The bare minimum for a sinatra app on cedar, running rack, and using bundler.

  $ git clone git://github.com/scottmotte/sinatra-heroku-cedar-template.git
  $ gem install bundler
  $ bundle
  $ heroku create -s cedar mywebapp
  $ git push heroku master
  $ bundle exec heroku open

  $ git clone git://github.com/scottmotte/sinatra-heroku-cedar-template.git
  $ gem install bundler
  $ bundle
  $ bundle exec foreman

Navigate to localhost:5000 | 5100

Add the gems to the Gemfile just below sinatra:

  gem 'sinatra'
  gem 'coffee-script'
  gem 'sass'

Run bundler:

  $ bundle

Create directories for your assets:

  $ mkdir views views/javascripts views/stylesheets

Require and assign the processors to your asset directories:

  require 'coffee-script'
  require 'sass'

  get '/javascripts/:script.js' do |script|
    coffee :"javascripts/#{script}"
  end

  get '/stylesheets/:stylesheet.css' do |stylesheet|
    scss :"stylesheets/#{stylesheet}"
  end

Restart your app and use your asset directories as normal.
ie. views/javascripts/test.coffee and views/stylesheets/test.css