You should do the Zero missions dude, although not required during the storyline, they are vital towards assets/100% completion. Here's the easy way to do supply lines:
First shoot the van closest to you, make it blow up. Loop around and kill the guy on the bicycle. Next go to the closest blip on the other side of the city, then after that do the last one. Get back to Zero's roof top as fast as possible. You'll jump for joy when you do it (the first time I did it I did, now I can do it in less than 4 minutes).
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