Cold A&W root beer served in those obscenely thick glass mugs they had at their drive-thru's (probably so they could be dropped without breaking. Frigging sugar heaven, man! I still crave the stuff.
I remember living in Kansas in the 70's before A&W was sold in stores. We'd go to A&W and get a gallon milk jug full of the stuff to take home.

I used to LOVE A&W root beer! Then I unfortunately developed some sort of allergy/sensitivity to a flavoring in root beer and I now get migraines from it. I hate not being able to get those giant ice cold mugs--we still have a super cool old-time A&W drive-in in my town! It just isn't the same when you have to order another soda. :(
I used to work at A&W and I hated it so much that I can never really enjoy the drink ever again.