Fuel from salt water ? I can't see that unless by using electrolysis.
As for algae -- maybe, but could it be grown in an area that we don't need for fuel?
You forgot to mention recaimed cooking oils -- nice thinking but but we'd have to compare the consumption of holidays by 'plane with consumption of fish & chips
Seriously, I understand that synthetics added to petrol/gasoline are starting to compete with grains for human consumption -- I don't think we could safely get all of our aviation fuel from the fields.