I went through the whole item database so you dont have to!
Items exclusive to the seasons. Seasons last 7 real-life weeks (49 days) each.
Spring
Resources
Clothing
Decor
Trinkets
Summer
Resources
Clothing
Decor
Trinkets
Autumn
Resources
Clothing
Decor
Trinkets
Winter
Resources
Clothing
Decor
Trinkets
Collectables
Gear