Sometimes, web publishers provide excerpt-only versions of their RSS feeds rather than offering the full text via RSS — requiring readers to visit the site for the full story. Web app WizardRSS converts any partial RSS feeds to a full feed.
If you follow a site for which you can't find a full-feed option, just take the site's partial feed, plug it into WizardRSS, then subscribe to the feed it creates in your newsreader for the full posts.
I tested WizardRSS on Lifehacker's partial feed, and while it had a few hiccups, in general it worked very well. Thanks Ste-V-illagE and Rosa!