They've been doing the Treasure Map since March, I think. It takes 21 days to get to the end, so you can miss a few days each month and still get to the end of it (it's always the same map). The blue treasure chests contain Premium items, while the Gold one contains a Super Premium. Those are the good weapons, armor, and equipment you want. The map seems to move to the next day at Midnight Eastern Standard Time, so just check in once a day to get your next step and reward.
If you finish the map before the month is out, each subsequent day rewards you with more credits, which can be used to upgrade items, play on the Happy Spinner, or to potentially buy power-ups during matches.
I think until the New Year they're giving 50% bonus XP for multiplayer matches, so if you're looking to rank up you can get a bit more points from each game.
And don't forget that playing with friends gains you extra credits at the end of rounds. Like always, if any CAGs want to play with someone, let me know. Cooperative mode is what I always play.