I just got the 100% completion achievement today. I hadnt been keeping track of which "random character" missions I had done so I was thinking I probably had a few of those to do, but it turned out all I needed as of today was to take Packie, Jacob, and Brucie to all the activities (eating, drinking, strip club, etc). So I knocked that out in like 15 minutes today and got it.
Waiting on the downloadable content now, I hope it's worthwhile. What I'd really like to see is more "maps" for the co-op modes like Bomb Da Base, Hangman's NOOSE, and whatever the other ones are.