Store and use prepared (canned) responses, per-project or globally.
For Redmine versions prior to 2.x, check out the pre-2.x branch.
The usual installation instructions for Redmine plugins apply. The (very brief) summary: Download or git clone to the plugins directory, run `rake redmine:plugins:migrate` to create database tables.
Enable the 'Canned Responses' module for projects you need this feature in.