I play triple triad while waiting in DPS queues. I am earning MGP fast and have all the cards that drop from NPCs who I have unlocked to play against. I just sell the cards that I already have. There are a few cards that only come from buying packs or from dungeons that I have yet to get but I am not worried. I'm in no rush. Maybe try it next time you are in a long queue and find yourself standing around. Might as well get some MGP while you are waiting.