Sam's robot is a small toy robot Ellie keeps, an automatic artifact in her backpack at the start of Lakeside Resort. Viewing it in the Artifacts menu makes Ellie speak to it.
Sam found the toy in Pittsburgh, but Henry made him leave it because they only took what they needed. Ellie quietly pocketed it and later gave it to him.
By the time Ellie handed it over, Sam was already infected and barely noticed it. After his death she kept the robot, and near Tommy's Dam she tells Joel she forgot to leave it on his grave. When you view it, she says she wishes she had said something different to him.
Braun's Firefly Pendant
Braun's Firefly pendant rests on a bench inside a gazebo next to the first cabin at the resort, in The Hunt section of Lakeside Resort. It belonged to Paul D. Braun.
Ellie's backpack
Ellie's backpack is an automatic artifact Joel picks up in the back of the butcher shop in Lakeside Resort. As he walks in, he grabs it from a low shelf, and it stays in his Artifacts menu from then on.
Joel & Sarah photo
The Joel & Sarah photo is a picture of Joel with his daughter, an automatic artifact in Ellie's backpack at the start of Lakeside Resort. You can view it from the Artifacts menu while playing as Ellie.
Kristof's Firefly Pendant
Kristof's Firefly pendant is inside a blue storage container in the coal mine during The Hunt section of Lakeside Resort. It belonged to Travis Kristof.