I just stick with the MP7, it only weighs three. I don't see how you can't carry other weapons, I usually can carry a MP7/Katana/AK47 or MP7/Hand cannons/Bullpup... to be honest the mp7 is tied for the second lightest weapon in the game, and I carry it while other perks sometimes. I have no problem using it to take out smaller zeds like clots/stalkers/crawlers/gorefasts and even snipe Husks and Bloats with a couple quick sprays to the head. I use the ak47/handcannons for fire power against larger enemies, and usually the katana against scrakes due to being able to stun them.