I'd second the suggestion of a Chromebook. Many in the 1KG/just over 2lb category and very inexpensive -- e.g http://amzn.to/2mCivvP -- and I thought I'd seen a few as light as about light as about 1.8lb; lighter than an iPad Pro 12.9 + external keyboard would be. They're extremely cheap compared to a decent laptop and often cheaper than a tablet + external keyboard. They're MUCH handier than a tablet + keyboard (let alone something like a Raspberry Pi + monitor + keyboard.)

The cheaper ones won't have as nice a screen as a mid-range tablet let alone the higher-end Apple/Samsung ones, but the lower cost and handiness for real work may make up for that for media consumption especially in a backpacking scenario where theft is a worry.

If durability is an issue, Dell, Lenovo and I'm sure several others make Chromebooks specifically for the education market. I got one from Dell Outlet refurb for about $150 (with a coupon; the current equivalent model is about $200), and while it's heavier than the consumer models models (about 2.75lb) it seems pretty close to indestructible.