Bounty hunting would be a good idea. But remember not to spam or to take the short cut. You can do signature campaign, twitter and facebook campaigns. If you are a good writer or a blogger, you could start with steemit and post your articles. You get Steem Dollars for upvotes which can be exchanged for bitcoins. For information, visit steemit.com
As you mentioned all can indeed get bitcoin in that way but which I often do at this time by participating in campaign signatures and tweeters and facebook campaigns because that's all I can do in my spare time.