For remote copies, https://archive.org/ can be instructed to keep a copy of a page, e.g.
https://web.archive.org/web/*/http://news.ycombinator.com/ to check for copies
https://web.archive.org/save/https://news.ycombinator.com/ to record a copy
These bookmarklets can be used to go from your current page to /web/ or /save/:
javascript:(function(){window.open('https://web.archive.org/web/*/'+(''+window.location));})();
javascript:(function(){window.open('https://web.archive.org/save/'+(''+window.location));})();
Unfortunately, this won't work on sites that robots.txt-block Internet Archive, and existing archives may be made inaccessible by a future robots.txt block.http://archive.is/ is another useful site that executes all of the JavaScript and captures the post-JS-execution DOM.