You will need a few things in order to make this trick work.

1) A MC Clubhouse
2) You need to have purchased a business from the ''Openroad network'' in your MC Clubhouse.
3) You need to have the business supplied and running.

Now ill tell you what you need to do in order to trigger the bags to spawn.

1) Wait untill your business made atleast $1000,- worth of stock.
2) go to the laptop within your business and select sell stock.
3) select the option that gives you the most money.
4) Now your character will be spawned outside*

*When the game spawns you outside to start the sell mission one of a few option may be active.
you're looking for the delivery mission where the game gives you and your friends a dufflebag.
if you get the plane/truck/helicopter/van mission as delivery method just destory them and try again untill you get the dufflebag mission.

While doing the sell mission with the dufflebags on you can swap between your saved outfits from the interaction menu. Make sure to select the outfit you want the bag saved on.

1) While wearing the outfit you want to save the bag to, go in to a Ammu-nation gun store
2) Walk up to the wall with the outfits.
3) Press the interaction button and from the shopping menu you can press the ''Save outfit'' button on your keyboard or controller.
4) overwrite the outfit you are currently wearing so that it saves the dufflebag to it.
5) Now complete the mission as normal.

Ones the mission is over you will earn the money like normal. If everything went as it should you should now have the dufflebag on your outfit. if the bag is gone, you can try resetting your outfit by going in to the interaction menu and putting a other outfit on and then going back to the outfit you saved the bag to. try this a few times. the bag should pop up after a 30 seconds.

http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=609231384
I can not 100% say for sure this trick still works. but if you want to read about it, go ahead

1) This glitch is only for the black duffle seen in the fleeca job heist.
2) I can personally confirm this trick to work, I tried it today (16th of october 2016)
3) I can confirm this to work on PC, I have not tried it on Xbox one or PS4.
4) Sorry for any Typo's or errors i made while typing this guide. ill try to fix them when i see them.
5) Questions can be asked below this guide.
6) Please note that rockstar can patch this whenever they want.