Most items in the game aren't required for you to proceed; challenge rewards are especially not required, although some guns and special gear here and there can make the difference between an easier experience and having less options. Some items are especially not required and will probably only add flavor to the world. An item that tells you how many HP enemies have left might be 'useful', but it's not doing much besides giving you data, for instance. There will be a fair number of 'useful' items too, so don't worry about it!
Time spent on the project so far: 388 hours
Currently working on: Moving on with the story