Depending how fit you are, you can run a generator with an exercise bike and make
100 watts easy for quite a while or 500 watts which will feel like a very steep hill.
You can watch TV and run a computer on that generator until you get tired.
A small TV and a laptop all day I suppose.
They used to make flashlights with no batteries but a trigger squeeze handle
that ratcheted a generator to light up the bulb. Now they have ones that you
shake for a while to charge the battery and then let some LEDs shine for a little while,
and also wind-up generator flashlights and wind-up radios for 3rd world countries
that can't afford batteries (and sold elsewhere as "emergency radios").
It is probably possible to make a human powered flashlight with two different metals
(copper and zinc-galvanize, held in wet hands)
and a circuit which is now called a Joule Thief, which is cheap and easy to make with
radio shack stuff, and is basically a flashlight that runs on a dead battery from other
flashlights for about a week using a simple homemade transformer to amplify the
last remaining fractions of a volt enough to power a super bright LED.
If not, a lemon will power that. But don't use the lemon, nor be a human flashlight
for much longer than experimental purpose or you may get heavy metal poisoning
since hands are slightly acid and electricity comes from chemical reactions in
batteries because chemistry IS an electronic phenomenon.