Many teams like to split roles among the group so that everyone can fit a specific archetype to the benefit of the team. Just make sure it's okay with them, first. When you've got money and feel it's necessary, throw down some armor, boosters, ammunition, or the like to your team. In fact, with the exception of Strike Packages and Equalizers (also known as your beloved sentry gun), all deployed items benefit your team. This can be further improved with the use of armor, which not only effectively doubles your resistance to damage (at max upgrade level), but also benefits your entire team when a cache of it is deployed. Putting it simply, unlike Treyarch's 'two hits and you're down' zombies mode, you're going to be able to take a lot more hits before eating dirt. Yeah, that's a health and armor gauge sitting down there, and it weirded me out initially, too. Take a look at the lower-left corner of your HUD.
