Ah for the days in the 1990s, when you could buy a laptop computer like the PowerBook DUO 280 with an active matrix grayscale LCD screen. It was a super legible screen in all situations but it was the best in direct sunlight without backlighting

I would create a minimal RAM Disk containing Mac OS with WriteNow or BBEdit. The hard drive would only spin up to save a file. I could run off battery for maybe 5 to 6 hours.