Updated 05-13-2016 02:19 AM
Near the end of One Shot, One Kill, when you get to the part where you must prepare for extraction, you need to toss some C4 around the white picket fence and put your claymores somewhere around the bumper cars and Ferris wheel. Then hide by the corner of the building by where you get the second intel in this section. The AI will almost always go towards the ferris wheel, and you can easily take care of the few who don't. The grenades that occassionaly come towards you won't hurt you (but you can move away if you feel safer doing so). Once the chopper lands, blow the C4, and sprint to Captain MacMillan. You will get shot a little, but you will make it to him and back to the chopper.
I had a lot of trouble getting through this section and tried many other solutions, but the other solutions just didn't seem to work for me. Thankfully, Deadly Minx told me about the following video by L0stH3r0
After struggling with the end of One Shot, One Kill for what seemed like forever, I watched this video and got it on the first time trying it.