6. Vance Astro
Michael Rooker is already playing Yondu in the film, but that doesn't mean there isn't room for another member of the original 1969 Guardians team. Vance "Major Victory" Astro would easily fit that bill. Even better, Astro could be a natural link between Quill's team and the future of the Marvel Cinematic Universe since that's exactly what he was in the comics. Astro is from the 31st century and while a featured role in the first movie is non-essential and out of the question, he'd make for an awesome Easter egg. Imagine the mystery and intrigue if Astro walked through the background of a scene with Captain America's shield on his arm. There's no need for an explanation why he's there, much less why he has the shield. The mere suggestion that someone not from the present is walking around in some corner of the MCU will suffice.