Anyone who does a lot of typing on the go would be wise to invest in either a cheap foldable BT keyboard (to pair with a phablet) or a slightly more expensive Chromebook.
But if you have a lot of money to spare, you might want to consider a Pomera E-ink typewriter. This is a line of super-portable devices with decent-sized keyboards, E-ink screens, and long battery life that you can fit in a pocket and get it out to write whenever you need it.
The Japanese gadget maker King Jim has been selling Pomera devices for several years in Japan, and now the company is launching a crowd-funding campaign to bring its newest model to the US market.
King Jim is launching the DM30 in the US, where they are calling it simply the Pomera. It features a 6" E-ink screen and a Japanese style folding 78-key keyboard. Screen resolution is a paltry 800 x 600 pixel display, but on the upside it does have 8GB of storage and an SD card slot, and it is powered by a couple AA batteries that are specced to provide 20 hours of runtime.
It does not have Wifi, but you can move files off via USB or QR codes (it can convert your text into a QR code somehow).
Retail price for the DM30 will be 43,000 yen in Japan when it goes on sale next month. The US price will be 55,000 yen (about $497 USD), but you can order one today in the Kickstarter campaign for 38,500 yen (about $348 USD).
$500 - or even $350 is a lot to ask for a typewriter, but I wouldn't be too quick to condemn the Pomera. It also supports a calendar feature, and a basic spreadsheet (saved as a CSV file). Also, the writing app has an outline feature and offers multiple font sizes and line spacing options.
King Jim is trying to raise around $90,00 in the Kickstarter campaign; so far they have raised twenty grand (in 3 days).