Windows: Planes, trains and automobiles—a long trip in any of them calls for some portable video. Any Video Converter, a longstanding favourite Lifehacker tool, is still being updated and working strong, recently adding 1080p YouTube videos to its repertoire.
There are lots of products that do some or most of what Any Video Converter (AVC) does, but few do them with the kind of bulk processing power that AVC offers. Load in a host of video files, choose a "profile" to convert to (mobile phone MP4, DVD-style video, etc.), and click Convert, then go find a sandwich place to walk to. When you get home, you've likely got a bunch of files waiting for you to load onto your phone, video device, or HTPC.
AVC also pulls down YouTube videos and converts them to your chosen formats, including support for the latest 1080p resolution. So when your friends ask you if you've seen "that video", you can say yes, even if you happened to be in a no-Wi-Fi hotel in the middle of nowhere at the time.
Any Video Converter is a free download for Windows systems only.