Fall has arrived, bringing cooler temperatures with it. Thankfully, Ember is running a sale through October 21st that takes 20 percent off many of its self-heating vessels — including the Ember Mug 2, a guilty pleasure of ours. The 10-ounce mug is available for about $104 ($27 off) with promo code SEASON20, while the 14-ounce version is down to about $120 ($30 off). The same code is good for the metallic versions of either model, too, as well as the 16-ounce Ember Tumbler (now $143.96)…