Imagine a Lone Wanderer carrying the following things - A backpack, two dual-handed rifles attached either side, and two smaller weapons carried on a belt. Its still quite a load, but is a reasonable amount that one person can carry, I think. Also, it forces us to make choices, and that's what Fallout is all about. By following this rule we should never have more than five weapons available to us in the Pip-Boy weapons list. That's right, if I can svck the fun out of anything, its Fallout.
This forces you to make decisions. You can't have everything since sacrifices will have to be made. It provides enough variety for every situation (long range, mid range, short range etc) while reminding us that our decisions have consequences. The key is finding the right balance.
Here's how it works -
Backpack weapon - Basically, this is any one of the available Big Gun family. I only called it a backpack weapon as some of them require a backpack to use (Minigun, Flamer, Gatling Laser) :shrug:. Any others, like a Missile Launcher or Fat Man are all fine, as they are so large they would have to be carried on the back, where the backpack would have been.
Two dual-handed weapons - This is any two-handed rifle/shotgun in the small guns/energy weapons category, which is affected by the http://fallout.wikia.com/wiki/Commando perk. You can choose to carry any two of these.
Two Holster weapons - This is any two weapons from the remaining smaller categories...
Melee - any of the available Melee Weapons...Police Baton, Baseball Bat, Combat knife, Shishkebab, Shovel, Super Sledge (ok, the last two are quite big, but to keep things simple we'll assume that they are possible to carry on the waist) etc
Unarmed - any Unarmed weapon...Deathclaw Gauntlet, Spiked Knuckles, Power Fist etc
One-handed firearm - This is any single-handed small gun/energy weapon affected by the http://fallout.wikia.com/wiki/Gunslinger perk.