On CentOS, to ensure that nginx starts on reboot run:
sudo chkconfig --levels 235 nginx on
Then for Unicorn to start on boot, you'd need to write an init script and save it to
/etc/init.d/unicorn
Here's an example one:
https://gist.github.com/mustafaturan/2762372
Make sure to change the variables at the top of the file to match your project. You'll then be able to start and stop your app with:
service unicorn stop
service unicorn start
And to make it run on boot, set:
sudo chkconfig --levels 235 unicorn on