A simple trick to auto-install missing gems when requiring:

alias old_require require

def load_gem(gem)
  old_require gem
rescue LoadError => e
  print "'#{gem}' can't be found, trying to install it..."
  system("gem install #{gem} --no-ri --no-rdoc")
  Gem.clear_paths() && require(gem) && puts("loading '#{gem}' ok!")
end

## Usage
ruby
> require 'xkcd'
'xkcd' can't be found, trying to install it..
Fetching: xkcd-1.0.1.gem (100%)
Successfully installed xkcd-1.0.1
2 gems installed
=> nil

Note: Use Bundler for proper dependency management. This is just a fun hack!