I would second the iPad mini. I had a full-sized iPad that I carried on a couple of trips. It was overkill, but useful. Great reading maps, and a long battery for capturing the daily GPS tracks, but a space hog. When I had to replace it, I got the mini, and it's been a much better touring companion. Fits easily in my handlebar bag. Still has decent battery life. I got it with the cellular chip because even when I'm not paying for extra cell service (which I usually do not -- although I'm more likely to when touring), I can download and save maps and use the GPS to navigate. Also, on my last couple of trips, I decided to spring for a data plan with a service other than my cell phone provider. The result was that I doubled the chances of being in contact with the outside world even when in the middle of nowhere. All respect to the people who want to "get away from it all," I like to stay in touch. My wife, who does not accompany me an most trips, prefers that I do as well. I sleep in a hammock and have a case with a flip cover. Flip the cover to the back, run some string through there and over my ridge line, and the iPad hangs right in front of my face. Great for obsessively tracking a nasty thunderstorm that I'm failing to sleep through. Or watching Netflix.
But, for strictly reading, a Kindle is cheaper, lighter, and easier on the eyes. There are cellular versions with the ability to have some internet/navigation/communication functions, but you won't be watching movies on it. I am as likely to read comics as books, so a color screen is essential, otherwise I'd be tempted to go that route.
And, of course, your phone can do all of that. There are trips where I don't plan on having enough downtime to make use of the iPad, and I just bring my phone. I have an Android phone, so this may not be an option for you, but I have done trips where I carry my Daydream View:
https://store.google.com/us/product/..._view?hl=en-US I don't know that the weight is that much different from an iPad mini, but it's easy to toss into a pannier. It's a fun way to get a big screen experience out of a phone, although resolution suffers. Also, last I checked, you could watch Netflix content using the Daydream, but you didn't have the same downloading options that are available for other devices. If I think I'm going to want to lie in my hammock and watch a video, Google Play seems to be the main service that lets me save videos locally for off-line viewing, although if you have video files in a standard, copyright-free, video format, there are other options.