I believe it tops as my favorite dessert, even above apple pie--and that's saying a lot! My Papaw and I used to eat them all the time when I was a kid, and he would give me the best part--"the icee." Lots of people try to pass off a good coke float. Sonic does this, for example. Theirs are awful. They include NONE of these recommendations for a perfect coke float. Okay, here we go...
First of all, you need good vanilla ice cream. NOT the kind in a cardboard box. It needs to be the kind in the plastic round container. It doesn't really matter what brand. It's the container. You see, cardboard doesn't allow it to stay as cold so you don't wind up with the same effect in the end. Okay, so plastic container vanilla ice cream.
Then you need COLD coke. Not lukewarm. Not hot. COLD.
Now this part is very important, and a lot of people miss this step. You need a good plastic cup. Not glass unless it's very thick glass. I don't know why this makes such a big difference, but it does. Try it and see. I also prefer my cup to be big and deep...you know, so I can eat more.
Okay so spoon in the ice cream and pack it down in there. Add some coke. Mix it up just a little. Add more coke. Eat until your heart is content...or until you feel you've sufficiently passed your recommended caloric intake. I'm at that point now. ;)