Depends on your metric. Sulfuric acid and iron is pretty simple if you don't count the blast furnace. Certainly a lot simpler than a gasoline generator. If you have grid power and a diode, electrolysis gets simpler --- though you probably want at least a transformer. Hydrolith is probably simpler and lighter than sulfuric acid and iron, though.
It's simple but surprisingly fickle, even more if you want industrial amounts of hydrogen safely. This is an example of a home setup and nontrivial considerations that went into it:
