cache_control: public
max_age:
  "assets/*": 2629000
  "*": 300

gzip:
  - .html
  - .css
  - .js

cloudfront_wildcard_invalidation: true

cloudfront_distribution_config:
  default_cache_behavior:
    min_TTL: <%= 60 * 60 * 24 %>
  aliases:
    quantity: 1
    items:
      CNAME: MYSITE

Should Fix:
Leverage Browser Caching

Setting an expiry date or a maximum age in the HTTP headers for static resources instructs the browser to load previously downloaded resources from local disk rather than over the network.

https://MYSITE/assets/images/AN-IMAGE.jpg (expiration not specified)
etc.
for images / stylesheets / js