Parts Kit?

Hey guys, I am building my parts kit for my main rifle, so far I have enough to rebuild the BCG 3 times(bolt, springs, extractor, ect.).

What I need help with is knowing what other spare parts I should get add to my box of parts. I mean what are common parts that would actually need replacing on the lower/upper(aside from barrel).

A couple of these since it’s being worked every time the weapon is cycling.

http://www.bravocompanyusa.com/Carbine-Action-Spring-p/spring%20carbine%20action.htm

The safety selector is also being manipulated a lot so maybe a spare one, or at least the selector detent and spring. Have heard of broken charging handles, something to consider. A couple of hammer, trigger, and disconnector springs. Spare set of gas key screws.

a few spare bolts, firing pins, disconnectors, gas rings, as well as the things stated from the above post

While attending courses I have found that having a assembled spare lower and BCG are particularly helpful. Trying to assemble or reassemble parts in the middle of a course of fire will most likely not happen in time for you to avoid missing a lot of valuable experience and information. Besides what you have mentioned, one part in particular that is worth having around is a spare stock. You wouldn’t think that they can break, but I can assure you that while not normally encountered, it can happen.

Why not just bring a spare rifle if possible??

Two is one. One is none. Isn’t that how the saying goes? Did you try a search on this topic?
http://www.google.com/search?hl=en&client=safari&tbo=d&q=+site:m4carbine.net+lower+parts+kit+m4carbine.net&sa=X&ei=PKnXUMXNC6Hm0gGk9YHABA&ved=0CDQQrQIwAA&biw=320&bih=413