[RedDevil]

6) and 7) might have a tiny beneficial effect, but only when the engine is hot and running under low load. The reason is that the water will evaporate and add volume to the intake air without adding oxygen, so it lowers the vacuum (or as you will increases air intake pressure) thereby reducing pumping losses.
Then, don't expect anything above 4% reduction of fuel consumption in the best conditions.

Mods that do have effect:
- Air up the tires to max pressure as indicated on the tirewall (but only on new tires or tires you know to never have hit potholes etc so you're fairly certain they do not have internal structural damage). Easy 5% mpg increase over OEM pressure on most cars.
- Flat closed hubcaps, front air dam, partial grille block.
- Remove unnecessary weight. Maybe even the spare.
- Use top tier LRR tires.
- Use narrow(ish) rims and high sidewalled tires.The smaller the rims, the higher the sidewalls with the same diameter.
- A block heater lets you start with a warm engine. This will vastly reduce pollution from cold running.
- Insulating the engine block makes it retain heat longer, so it is warmer on the next start.
- Same for insulating the whole engine bay. But beware, lead acid batteries should not get too warm.

Especially, forget about 'HHO'.
Splitting hydrogen from water by electrolysis is frightfully inefficient, reason why commercial hydrogen production does not use electrolysis but rather scrubs hydrogen from natural gas, burning off the carbon in the gas as a side effect. Inefficient too, but still cheaper that electrolysis.
If you do see any gain from your bubbler, it may just be due to the moisture that comes with it (see 6) and 7)) so feeding the bubbler with a regular aquarium pump might yield the same effect, if not better. And it won't detonate ever.