This is a good post, becasue it addresses some of the issued I've faced with my kits. It seems that I'm forever re-configuring and re-packing my kits depending on the situation, and as a result, I've gone 100% modular with all the parts to the kits.
Thus, I have a FAK in one small bag, a "Food & Water" bag, a "Shelter" bag, and so on.
Yes, it adds weight overall, however, when I'm throwing a bag together for a trip to Long Island, I really don't need a fishing set, I can't carry ammo, and I see no need for extensive signalling when I'm in an urban setting. A pair of GMRS radios does the trick, as does a small Ham radio.