Chest 1 (Element of a compound bow)
In the skating rink, where there are two semicircular, orange tents.
Chest 2 (Element of a machine gun)
A bit past the skating rink, go right. The chest is among trees, at the wall.
Challenge- Scorched earth (Destroy 4 fuel tanks)
You find it in the meadow, where you meet two opponents for the first time, during the main storyline.
This truck is in the forest, which you cross on your way to the Trinity HQ. Around, there are several opponents.
After you exit the area of the frozen lake, in the next meadow, you find a big group of opponents. One of the vehicles, by which they are, is the next target of the challenge.
Before you zip down the line, you can aim at the barrel next to the truck, while standing on the platform, on which you get while going to the prison bloc.