Here’s the Sharp PC-1300S - you’ll need a capacious pocket:
It has a not-quite-Basic programming language, but it’s capable enough: “calculates and prints the first 229 decimal digits of π in about fourteen hours”
The display is bright and readable. The electrostatic printer is fast and puts on quite a light show in a darkened room, not to mention being noisy. Neither allows for arbitrary graphics, being limited to the included character set.
The machine comes with a hefty book listing about 150 programs running the usual gamut from math to surveying to circuit analysis to games.
There’s a glorious photo of the author on this nearby page.
See also the ‘handhelds’ tag.