Regarding Images: on the Google Page speed results page, you can download optimised images at the bottom of the page. There’s a line below the Passed Rules section which says “Download optimized image, JavaScript, and CSS resources for this page.”
Regarding Javascript: Google will be referring to the Webflow & JQuery scripts which are a part of your site. These are essential to functionality so can’t be removed.
Its always worth taking Google PageSpeed with a pinch of salt. While its a good general indicator to how fast your page will load there’s also a bunch of other factors to take into account like the speed of your server (Webflow use Amazon AWS which is pretty damn fast) and so on…
Its also worth running your site through speed tests from Pingdom (http://tools.pingdom.com/) and Gmetrix (https://gtmetrix.com/) which will give you a more rounded view of how fast your site is.