The Friend Request exploit is all I've tried so far, and I love it.
I found some things out that would help some people above -- You can still go to Michael's safehouse and change into any clothes you own, including putting on masks (he'll always be carrying the backpack unless you get on a motorcycle). You can also pull out your guns and shoot in safehouses, but unfortunately the family doesn't appear.
Any cars you put in Michael's garage before replaying the mission will still be in there (hangars don't work though).
You can go into Franklin's Aunt's house (she is not there), and even the garage will open for Michael! It STILL had the car I lost in that garage when Franklin upgraded to Vinewood hills. Also, yes you can go in the Vinewood Hills house, but it's not decorated for Franklin and the garage will not open for you. I bet Trevor's garage will open for Michael as well, but I didn't try it. The parking spots at the strip club unfortunately won't spawn their stored vehicles.
You can even shoot and rampage inside the strip club, although the funniest part about that place is how you can go in peacefully and see the patrons just watching the stage and clapping even though there are no strippers.
You can't shoot inside Ammu-nation, it acts normally and I'm sure the other stores do as well.
This isn't part of the exploit, but I took one of the big jets from the airport and was flying over the marina... Decided to dip down to see if my stored boat would appear at my slip (it does not)... I got too low and was about to run into the buildings, so I bailed, and managed to come out right onto a rooftop as the plane exploded. I lost some of my armor but I was fine!
I love shooting the minigun with that backpack on my shoulder. It makes it look like that's where the bullets are feeding from.
Edited by xenorama, 6 days ago.