3D movies can be annoying at best, and painful at worst. For a few bucks, you can grab a pair of 2D glasses that will let you see 3D movies without being subjected to all three headache-inducing dimensions.
Hollywood seems to really be pushing this 3D thing, to the dismay of myself and many others. If your friends are dragging you to see a movie in 3D, or if the theatre's only offering a particular movie in 3D, you can save yourself the pain by picking up a pair of these 2D glasses. They look just like the 3D glasses they give you at the theatre, but block out one of the images so you see it in good, old-fashioned, non-headache-inducing 2D.
You can, of course, always try and make your own at the theatre, but depending on the glasses those lenses can be hard to pop out, so $US10 is a small price to pay for moviegoing freedom.