I just got my first smart phone... moto G through republic wireless which uses the Sprint network. It weighs 5.1 ounces and the charger weighs 1.5 ounces. My old dumb phone was lighter at 2.75 ounces. But the Moto g will replace the paperback books I usually carry (which weigh anywhere from 4-8 ounces) and probably my notebook/journal. The voice to text feature could be useful for journaling but I'm not totally sold on that idea yet.
Although I may read on the phone, audiobooks are a good substitute with the advantage of using very little battery compared to reading and being a passive activity I can do lying down in my tent. Reading in my tent is sometimes awkward and uses up headlamp battery.
I wouldn't personally carry a tablet. If I felt like I need more screen space, I would consider a larger phone. Moto g has a 4.5 inch screen.