Quick and dirty multiple file editing in one window for TextMate - Add the command to a bundle (I use source) with: keycombo ⌘S, save document, discard output. Upon saving a file with the 'scratch' extension the script will parse out all the included files and write them to disk IFF they are in the scratch file's directory or a subdirectory thereof

command.textmate

#!/usr/bin/env ruby

require '[..]/scratch_file.rb'

if (file_name = ENV['TM_FILEPATH']) && File.extname(file_name) == ".scratch"
  ScratchFile.new(file_name).write!
end

example.scratch

#file "models/post.rb"

class Post < ActiveRecord::Base
end

#file "controllers/post.rb"

class PostsController < ApplicationController
end

#directory "tests"
#file "models/post.rb"

class TestPost < Minitest::Test
end

scratch_file.rb

#!/usr/bin/env ruby
require 'fileutils'

class ScratchFile
  DIRECTORY_REGEX = /^#directory "((.+\/)*[^\/]+)\/?"\s*$/
  FILE_REGEX = /^#file "(.+)"\s*$/
  
  def initialize scratch_file_name
    @scratch_file_name = scratch_file_name
    @working_directory = File.dirname(File.absolute_path(scratch_file_name))
    @directory_prefix = ""
  end
  
  def write!
    files.each do |name, lines|
      if should_write_file name
        FileUtils.mkdir_p(File.dirname(name))
      
        lines = lines[1..-1] if lines[0] == "\n"
        lines = lines[0..-2] if lines[-1] == "\n"
      
        File.write(name, lines.join)
      else
        puts "!! Warning: File #{name} is outside the working directory (#{@working_directory}) of the scratch file. File NOT written."
      end
    end
  end
  
  def files
    {}.tap do |files|
      current_file = nil
      
      each_line do |line|
        if new_directory_prefix = new_directory_prefix_for_line(line)
          @directory_prefix = new_directory_prefix + '/'
          current_file = nil
        elsif file_name = new_file_name_for_line(line)
          files[file_name] = (current_file = [])
        elsif current_file
          current_file << line
        end        
      end
    end
  end
  
  def each_line &block
    File.foreach(@scratch_file_name) do |line|
      block.call(line)
    end
  end
    
  def new_file_name_for_line (line)
    if new_file_name = line[FILE_REGEX, 1]
      return File.expand_path("../#{@directory_prefix + new_file_name}", @scratch_file_name)
    end
  end
  
  def new_directory_prefix_for_line (line)
    line[DIRECTORY_REGEX, 1]
  end
  
  def should_write_file (file_name)
    File.dirname(file_name).start_with?(@working_directory)
  end
end

Obviously this only works one way. My use case is to quickly build out new classes and the appropriate tests, each in their own files, and edit them together, only having to switch windows to run the tests. I'm not sure if/how I should extend this to keep the scratch file up to date with changes to the individual files, but as it's not intended for "ongoing" use that's not a big concern.

Added ability to specify a common directory, to avoid typos. I avoided refactoring the class this time but if it gets any more complex I just might.