Steps to Show Random Posts with Thumbnails and Posts Summary in Blogger

Step 1. Login to your blogger account, select your blog and go to Layout.

Step 2. Add new widget by clicking on the Add a gadget link and select Html/JavaScript from the popup window.

Step 3. After adding the Html/Javascript you need to grab the following code with styles attached.

 <style>
#random-posts img{border-radius: 10px;float:left;margin-right:5px;
width:75px;height:75px;background-color: #F5F5F5;padding: 3px;transition: all 0.2s linear 0s;}
#random-posts img:hover{opacity: 0.6;}
ul#random-posts {list-style-type: none;padding: 0px;}
#random-posts a {font-size: 12px;text-transform:uppercase; padding: 0px auto 5px;}
#random-posts a:hover {text-decoration: none;}
.rp-snippet {font-size: 11px;background: none; padding: 5px; margin-right: 8px;}
#random-posts span {}
#random-posts li {margin-bottom: 10px;border-bottom: 1px solid #EEEEEE; padding: 4px;}
</style>
<ul id='random-posts'>
<script type='text/javaScript'>
var rdp_numposts=5;
var rdp_snippet_length=110;
var rdp_info='yes';
var rdp_comment='Comments';
var rdp_disable='Comments Disabled';
var rdp_current=[];var rdp_total_posts=0;var rdp_current=new Array(rdp_numposts);function totalposts(json){rdp_total_posts=json.feed.openSearch$totalResults.$t}document.write('<script type=\"text/javascript\" src=\"/feeds/posts/default?alt=json-in-script&max-results=0&callback=totalposts\"><\/script>');function getvalue(){for(var i=0;i<rdp_numposts;i++){var found=false;var rndValue=get_random();for(var j=0;j<rdp_current.length;j++){if(rdp_current[j]==rndValue){found=true;break}};if(found){i--}else{rdp_current[i]=rndValue}}};function get_random(){var ranNum=1+Math.round(Math.random()*(rdp_total_posts-1));return ranNum};
</script>
<script type='text/javaScript'>  
function random_posts(json){for(var i=0;i<rdp_numposts;i++){var entry=json.feed.entry[i];var rdp_posttitle=entry.title.$t;if('content'in entry){var rdp_get_snippet=entry.content.$t}else{if('summary'in entry){var rdp_get_snippet=entry.summary.$t}else{var rdp_get_snippet="";}};rdp_get_snippet=rdp_get_snippet.replace(/<[^>]*>/g,"");if(rdp_get_snippet.length<rdp_snippet_length){var rdp_snippet=rdp_get_snippet}else{rdp_get_snippet=rdp_get_snippet.substring(0,rdp_snippet_length);var space=rdp_get_snippet.lastIndexOf(" ");rdp_snippet=rdp_get_snippet.substring(0,space)+"&#133;";};for(var j=0;j<entry.link.length;j++){if('thr$total'in entry){var rdp_commentsNum=entry.thr$total.$t+' '+rdp_comment}else{rdp_commentsNum=rdp_disable};if(entry.link[j].rel=='alternate'){var rdp_posturl=entry.link[j].href;var rdp_postdate=entry.published.$t;if('media$thumbnail'in entry){var rdp_thumb=entry.media$thumbnail.url}else{rdp_thumb="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHO6YTfU9ZJccuYeL1I45ECpqodaBR3w440V6Akly7KhIKeREtF7hU1lafMeVL1j3nuphsEtv34po6Ih8v3eXuPB-KjKw3vq6g5LS33-SL5jbHzcSw9F7-5AsFC5kpt22TSLsIX8MnMaM/s1600/no_thumb.png"}}};document.write('<li>');document.write('<a href="'+rdp_posturl+'" rel="nofollow"><img alt="'+rdp_posttitle+'" src="'+rdp_thumb+'"/></a>');document.write('<div><a href="'+rdp_posturl+'" rel="nofollow" title="'+rdp_snippet+'">'+rdp_posttitle+'</a></div>');if(rdp_info=='yes'){document.write('<span><div  class="rp-info">'+rdp_postdate.substring(8,10)+'/'+rdp_postdate.substring(5,7)+'/'+rdp_postdate.substring(0,4)+' - '+rdp_commentsNum)+'</div></span>'};document.write('<br/><div class="rp-snippet">'+rdp_snippet+'</div><div style="clear:both"></div></li>')}};getvalue();for(var i=0;i<rdp_numposts;i++){document.write('<script type=\"text/javascript\" src=\"/feeds/posts/default?alt=json-in-script&start-index='+rdp_current[i]+'&max-results=1&callback=random_posts\"><\/script>')};
</script>
</ul>

Step 4. Just paste this in the widget area and give widget the title of "Random Posts".

Random Posts Options

- Thumbnail dimensions: to change the size of the thumbnails in pixels, replace the 75px value.
- Summary length: you can control the the length of the summary (in characters) by changing the 110 value from var rdp_snippet_length=110; 
- Post info: if you want to hide the post date and comment count change 'yes' from var rdp_info='yes'; to 'no';
- Font Size for Posts Titles and Summary: to modify the font size for the post snippet modify the 11pxvalue and for the posts title, the 12px value;

Step 5. Click on the Save button and you're done! Your sidebar will display a random posts widget on each of your blog pages.