Wikipedia might not always be the most accurate source of information out there, but it is one of those things that I'm constantly thankful is around. You can actually ensure that the site is always there for you, even when you don't have a web connection, by downloading it in its entirety.
We wrote about a way to do this with an open-source app called XOWA last year, but the process is actually even easier.
Wikipedia creates a download of its database on a regular basis that is literally just sitting there for you to download it. The site file is available to anyone who wants it, and it can be used for "mirroring, personal use, informal backups, offline use, or database queries."
Right now the whole file is 14GB of data compressed, or 58GB uncompressed, well within the confines of USB stick capacities. All you have to do is go to this site and download it, saving it to the USB Drive of your choice (I recommend a nice Yoda one).
It's one of those things you're not sure you're going to need until you do, but when the internet as we know it ends (or you're just travelling without WiFi), and you really need to know how many episodes of The Golden Girls there were (180), you'll be happy you have tucked away.