I'll be compleatly honest, this is a very hard achivement to do.
I was lucky and got it when I was in a pub group in my first 50 hours.
But reacently I was helping a friend get it and it took ages and I mean AGES.
Different people will tell you different methods, but this is how I do it.

Ok right off the bat you need 8+ bags.
So you can cross off Rats Day 1 as the max bags you can get is 7.
The heists that work are:

Nightclub
But about 50-75% of the time there won't be 8 bags. It's best done on Overkill for there to be a chance for 8 bags. There also has to be atleast 4 bags of coke, since there's a maximum of 4 money bags. Even with the loot drop truck, the bags will spawn with you during the escape. There's an annoyingly low chance of escape on this heist, but it's easy/fast enough to keep retrying. Just remember to leave during an assualt wave for the highest chance of escape.

Rats Day 2
If you got Overpass escape day 1, you can get Garage for day 2. Day 1 cook as much as you can, 7 is the max, and hope you get the right escape (as you can't get the same escape 2 days in a row).
Day 2 you have to steal the meth back and that will give you atleast 8 bags, counting the money for the meth. In the case of them betraying you, there will be money stacks in the same room as the intel safe, with a chance of another in a safe somewhere. This should give atleast 10 bags with 8 being superlight. The only downside is that you have to cook 7 bags, which can take a very long time and will make for an angry team if the wrong escape happens or it doesn't happen. But unlike the other heists, this can be done on any difficulty. But if you want to make some money for your time, you may want to do it on Very hard or Overkill for the cash.

Transport Harbour
Like Nightclub, this has to be done on Overkill so there's enough bags (it can be done on lower difficulties, but there is a much lower chance of enough bags). Bring a saw and some C4 to speed it up. Best loot type is jewelery, money then gold. But you're kinda stuck with what you have unless you want to keep restarting. Still this one is my pick if you have a full high level team that work well together. This one does require one person to own the Armoured Transport DLC, most people do but some don't.

After triggering the escape
If all goes well , you should get the escape with 8+ bags. You have limited time to get the bags up. All the doors can be picked, C4ed and sawed so one person should run ahead and clear the path as the rest daisy chain the bags up. If all goes well you should make it in time. This is the easy part, the hard part is making it happen.

Another kinda short guide.
I know alot of people who had a ton of trouble getting this achivement because it's so hard to trigger. This is one that works better with atleast 3 people, since you have to get so many bags moved. Still this works 100% of the time but the chance of getting it is very very low. Basically you just have to keep trying until you get it.

If you're having trouble getting the escape to trigger rember to kill civis and leave during an assault for the best chance.

I have more of these achivement guides in the works but I'm happy to take suggestions.