We Don't Drink, We Don't Chew, We Don't Go With Girls Who Do

What does it mean to watch out for the weaker brother, not to put a stumbling block in his path?

Does it please God if we abstain from certain foods and drinks?

Is sanctification about avoiding the things of the world?

Should a Christian abstain from certain foods and drinks even if he believes he is not Biblically required to, because he is watching out for the weaker brother?

What IS a weaker brother?