Here's my take on 'you gotta give it away' from Last Night On Earth...
Throughout the song, the lyrics point to the idea that the female in the song, 'she', is living a life that is free, without many restraints and nothing holds her back, almost without abandon. But, she still has a conscience 'She knows just what she's worth still she's living like its the last night on earth'
From the intro of the live Popmart version, 'Went looking for spirit but found alcohol'... The wise choice could be made to follow what the soul needs, yet falls for the temptations that physical life leaves for us. I think Bono himself goes through this a bit as I bet he's met his temptations several times as a pop icon, and having to make a conscious decision or just letting it all go and not caring how he treats himself or others.
'You gotta give it away' preceeds 'she knows it hurts but we're living like it's the last night on earth' which is sorta saying that it is taking a toll on her, so much that it hurts, yet she still wants to give into whatever makes the rest of her pains go away, and to have no regrets that life wasn't lived fully. If it was your last night on earth, would you contemplate or let go of it all and live thinking that your actions today have no consequences or bearing on tomorrow?
So to answer the question, I think 'you gotta give it away' is saying that you have to give up the temptations, give up the lifestyle that fails you time and time again to recognizing your real needs and the reality of life surrounding you.
Just so I don't come across as boring as f*ck, living like its the last night on earth isn't an evil though. Just listen how awesome the song is, has a great tempo and is catchy as hell. If Bono and the Edge or whoever contributed to the lyrics were recalling times when they let their guard down and had drunken crazy night, look at the results they've created.