what does "When the gong sounds, get the hell out of there. You're neither of you to the blood bath at the cornucopia. just clear out put as much distance as you can between yourselves and other, and find source of water, he says. Got it?" this quote mean

This is Haymitch's advise to Katniss and Peeta. He knows the Cornucopia is more or less a trap. The longer they stay trying to find an item, the more likely they will become a casualty in the ensuing blood bath. Haymitch's advise is to spend as little time waiting to be killed in the Cornucopia and get into the jungle. 

Haymitch is telling Katniss and Peeta to not fught in the Cornucopua because they are more likely going to be killed trying to find something. He tells them just run and find water than make the plan.