The best way I found to achieve this was the following..
1- Complete game with Sora collecting as many moogle points and cards in the rooms as you can, no need to spend. Now save. You should have enough MP and cards collected for the achievement.
2- Open a moogle shop, sell all your cards and buy all the packs.
3- Open a new moogle shop in next room, sell all your cards and buy all the packs.
4- Rinse, repeat, pop.