Squad Traits is a short supplement for FIST that adds modifiers to the entire team of PCs. These modifiers range from making the game harder, to making it easier, to making it weirder. Think of them as a slider that controls the game's micro-genre.
The PDF is 2 pages, with a bare but readable layout. There's no art or cover, but the content is solid.
Overall, this is a really clever idea and fits naturally with most FIST games. I think a lot of third party content tends to work well as standalone material, but this is a rare example of a mechanic that I think belongs in the core book.