"Yeah, the material's been good so far, although I'm sure there's got to be a drought coming someday"

In this quote, John Goodman is expressing his complete satisfaction with the material he has actually been given up until now. He acknowledges that it has been great, but also acknowledges that there might come a time when the quality of the product might not be as excellent. By stating "there's got to be a drought coming at some point," he is suggesting that there will likely be a time period where the product might not be as plentiful or as excellent as it has actually been. This could be a recommendation to the cyclical nature of the show business, where there are highs and lows in terms of the quality and amount of work available. In general, Goodman's declaration reveals his gratitude for the existing product while likewise acknowledging the capacity for future difficulties.