I've seen a number of small polybags in stores branded LEGO xtra. What are these?
LEGO xtra is a theme of sets that focus on adding play value to your existing sets by providing accessories or play areas.
For example, LEGO xtra Traffic Lights adds 4 buildable traffic lights and a few associated accessories to your city streets:
These sets sometimes feature playmats or baseplates as well, such as the Sea Playmat set:
These sets are reminiscent of the older accessory packs that used to be available some time ago:
LEGO was kind enough to send me a copy of Sea Accessories (40311).
Here are the included parts:
Overall, this is a nice variety of parts that should add to the playability of a beach, marina, or even pirate hideout. If you already have a large collection, there isn't much terribly exciting in there, but I do appreciate the blue and yellow dual-injected bird.
The price per piece of these sets is unfortunately not great. This one is $4 USD for just 24 elements, but the parts that you get are a bit more unique than those found in the Classic parts boxes. They have a focus on adding play value to your existing sets, and often feature larger elements such as animals or vehicles that tend to be more expensive and more add interest to models.