Objects represent both light and heavy items characters might find on a battlefield. Objects can be placed, picked up, held, and put down. Multiple objects may be in the same square.
At page 4, game setup step 3, it is said:
The first player must first place all of their characters in their starting area squares, and any non-object additional game elements either in their starting area squares or off the map as appropriate. The second player then does the same.
The first player then places all objects on their starting force. These objects must be placed in squares outside of any starting area. The second player then does the same. (See p. 25 for Objects.)
Can I stack objects in the same square at Step 3?