Nginx and Apache have built in caching which can usually be easily enabled, which while arguably not as fast as using Varnish (Nginx in particular will serve cached content from disk using sendfile, as opposed to Varnish's in-memory caching) are still faster than calling back into PHP.

PageSpeed is 1 liner installation on your instance. It will compress assets etc automatically as Apache serves them. Worth adding to your deployment script.

Nice. I like how it could be installed in Apache, and then left to its own devices.