This is a quick and dirty way to find the most requested static resources of your site (e.g., images or javascript files), using Unix shell commands:
grep -oE "GET /[^ \t]+\.(gif|png|js|css)" /var/log/httpd/access_log \
| sort | uniq -c | sort -nr
Use the correct path to your system’s HTTP server access log.
You can of course also add or replace extensions, to your heart’s content.