you have a few options. one is if you have been creating your application properly, you should have migration files to send to your friend. These at least would give the structure of your database. Then you can get the plugin ar_fixtures and use that to copy all of your current data into fixtures. then you can send your friend your migrations and fixtures and he can run the rake tasks (rake db:migrate and rake db:fixtures:load).
Otherwise, hopefully your friend is using the same type of database that you are. For instance, if you’re both using MySQL you can just dump your schema to a file and send that to your friend so that he can import the structure and data into his database.