A.rb

Rails::Initializer.run do |config| 

  # Require the latest version of haml
  config.gem "haml"

  # Require a specific version of chronic
  config.gem "chronic", :version => '0.2.3'

  # Require a gem from a non-standard repo
  config.gem "hpricot", :source => "http://code.whytheluckystiff.net"

  # Require a gem that needs to require a file different than the gem's name
  # I.e. if you normally load the gem with require 'aws/s3' instead of
  # require 'aws-s3' then you would need to specify the :lib option
  config.gem "aws-s3", :lib => "aws/s3" 
end 

B.rb

Rails::Initializer.run do |config| 
  %w|haml chronic hpricot aws-s3|.each do |gem|
    config.gem gem
  end
end