I am having difficulty opening and retrieving the items from the chest at the end of mission 2. Is there a specific marine that has to pick up the relic? They both of red symbols as though I am not able to pick them up.

Also I read that assault squads are able to use jump packs. Is this only later in the game or did I miss something?

edit: Found out there was a chaos marine on the very edge of the map that needed to die. Still wonder about the jetpacks though.

You have only one assault squad. I believe it's available after you complete the 2nd mission. Assault squads are by default equipped with a jump pack. Be wary though: sometimes it's difficult to use them, especially in areas with lots of obstacles.