First off, two things: the movie Gravity is likely the most realistic space travel-based movie ever made, and I'm about to spoil the crap out of it by revealing one huge flaw. So, if you don't like spoiled movie, you may want to leave. Okay, there's your fair warning. Everyone else, come along!
Now, there's already been a number of sites pointing out flaws in the science of the movie, and while it's incredibly accurate in many ways, there are some issues. Various sites have pointed out the phantom magic hatch on the Soyuz' re-entry module (though, to be fair, it does match with one on the Soyuz simulator), the inaccurate orbital locations of the three main locales of the movie (Shuttle/Hubble, ISS, and a hypothetical future version of Tiangong), and, most importantly, the fact that under a spacesuit astronauts wear bulky cooling garments and a diaper, not sexy athletic-gear underthings. Unless you think adult diapers are sexy.