If I have a few mins to kill during the day (usually when waiting for ETH/BTC to hit the exchanges from my wallet) Ill sign up for an airdrop or two. Most of the ones that I have either haven't hit exchanges or are worth under $1.
TRON (TRX) was the first one for me that actually did something.
500 free TRX peaked at ~$30 and is currently worth ~$19
HODLing!
Great of course. The man already wrote that he participated in 150 airdrops in six months. For all the time he got about 2-3 ETH. While one was very profitable at $ 1000