The first two titles in the Dead Space series didn't offer much in the way of collectibles. For the most part, you spent much of your time either evading or surviving encounters with undead necromorphs—creatures of living and dead human tissue, re-purposed by the alien Marker into killing machines.
Dead Space 3 offers much more breathing room than its predecessors, and allows you to go off the beaten path to do your own thing while pursuing the game's main objectives. With that in mind, the game's developers at Visceral have added a number of new optional objectives in the form of collectible items that you can acquire throughout any extensive playthrough of the game.
The following videos will help you to locate these items throughout the game's many chapters.