Here is the list what comes with Summer DLC:
- 3 new biomes: Sand, Stone and Jungle Islands you can explore during your adventures!
- 2 new base resources: Cactus and Bamboo
- New furnitures you can craft with new materials
- Fish trap for automatic fishing process
- Cactus fruit maker and cactus salad
- 3 new species of fishes: Stone Fish, Sand Fish and Jade, each one unique for new biome

More details on the official game page of Summer ...