Oh hmm, I just use my phone for that. It doesn't seem worth having an additional, limited purpose device. I assume a 7" e-reader is too big for a pocket.
The Inkplate 10 isn't pocketable but it's very light, easy to put in your backpack or whatever. I just wish they had a 13" version. The 13" Ipad Air is really very nice if you don't mind Apple products.
There are also some folding phones now with largish screens. A buddy of mine has one and it's nice. Too expensive for me though, and it's more Android.