Along with the characters, who have been the main focus of all the reports on Suicide Squad thus far, there are a great deal of great story arcs from the comic books that the film could draw upon. The general concept is, obviously, very much drawn from World War II movie The Dirty Dozen, so its possible the plot of the Suicide Squad film could very much do the same; one of the great concepts they could pinch from John Ostranders classic run were the examinations of the teams psychological make up by the teams therapist at the end of each mission. There are also specific storylines that could easily translate into a ninety minute action flick. The first few arcs in the Ostrander run touched upon political issues that are still relevant today, with the Suicide Squad sent to deal with threats in the Middle East (a terrorist group called the Jihad, no less) and Russia, or the later - slightly more comic book-y - run of issues where Poison Ivy and Deadshot are recruited to the team to help assassinate a bad guy whos raising a zombie army. Most recently a whole mission was about tracking down an AWOL Harley Quinn, who believed The Joker was dead, which would be a pretty great introduction.
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/