what does estragon means when he says, "There's no lack of void?"
Estragon seems to be the more thoughtful of the two men, but that does not mean he is thoughtful to the level that we might expect of humanity. Clearly, time and place have changed into a state of nothingness, a nothingness in which these characters have to live for whatever reason. They seem to feel a void, meaning that they have the vaguest of recollections of their previous existences but that those memories are so amorphous that all they have now is a void, a state of nothingness or emptiness where something should be.
For example, most conversation progresses from a natural starting point to a natural ending point. Yet, the reader notices that with Estragon and Vladimir, conversation is stilted, circular and nonsensical. This is a void in what used to be a common pastime for human beings. The fact that Estragon recognizes these voids is significant because it shows that he understands it is not natural and not hopeful for his future.