Just go to the post office and say you do not want any third class mail. MOST junk mail is sent via third class so you would not recieve much of that stuff.
Junk mail is like ads on TV--it pays for the "good stuff" that shows up (like IRS refund checks, letters from kids,Dads and Moms, packages from Ebay, etc.) And--if you think people don't appreciate getting mail delivered 6 days a week--just remember the outcry when the USPS merely mentioned the possiblity of eliminating Saturday delivery. People had FITS!!
I just recently retired from the USPS--worked for over 17 years in my little town--and our rural carriers are very much appreciated because they do their very best to deliver the mail. Sure they make boo-boos every once in a while, but they are not rude and lazy, nor are the clerks who sell the stamps.
And--as was posted by the wife of a carrier on an earlier post--Postal workers are under Social Security (since 1985), and if the Republicans really wanted to push "private Social Security accounts"--they could remind EVERYONE that ALL Federal employees (including Congresscritters) are eligible to have TSP accounts. They are a VERY GOOD thing!