Anything other than signature campaigns and gambling.
A bit saved is a bit earned. So save your money by not clicking on any of the signatures of the people posting in this thread.
if you do not want to play in bounty campaign or clicking then I think you can buy mining tools like S9 and other antminer which will give you bitcoin as much as mining tool you have. I think that's all you can do if you want to get bitcoin without working.