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 ~$19
HODLing!
WOW. there growth is impressive. i did signup for airdrop campaigns but i did not make much only 0.18$ . the funny thing is that the coins keep depreciating in value.. so right now i'm not wasting my precious time for that..