>>2563028nintendo dsi or ds lite + gba and ds flash cart,
or a gameboy sp with a backlight mod is also acceptable.
those are the endgame /out/ devices. they have massive battery life, they're pocketable, they're oldschool nintendo quality products that can be thrown around, they fit in a pocket, and they have a clamshell design to protect the screen.
the 3ds and switch are too easily breakable outdoors.
chink emulator handhelds are getting good but the build quality isn't older gameboy level so they're not as good.
when i was a kid in boy scouts i had a sega gamegear and a gameboy pocket.