Some helpful code from the Amazon Elastic MapReduce developers is up on GitHub now for you to download. This includes several sample apps and some bootstrap actions for popular applications.
The sample apps will teach you how to build apps with Pig, Hive, Node.js, Powershell, and more. The bootstrap actions are shell scripts stored in Amazon S3 that Amazon EMR executes on each node in your cluster. More from the GitHub page:
Bootstrap actions execute as the Hadoop user by default; they execute with root privileges if you use sudo. From the EMR Command Line Interface you can reference a Bootstrap Action as follows:--bootstrap-action "s3://myawsbucket/FileName" --args "arg1,arg2"
For more information about EMR Bootstrap actions, see http://docs.aws.amazon.com/ElasticMapReduce/latest/DeveloperGuide/emr-plan-bootstrap.html