I have books on my Kindle with content that would probably make them ask more questions. It is nothing illegal or even questionable in most countries, but it would lead them to ask questions I don't want asked. I have similar content on my smartphone.
Also, do they check normal pen and paper notebooks? Like do they flip through them and read them?
I'll be carrying them on and traveling on a tourist visa if that makes any difference.
Edit: I don't know if it makes a difference, but I'm flying into one airport in China then getting a connecting flight to another domestic airport.