What weapon do you have on you at all times? No matter the build... there are some weapons you just dont leave home without.
For me it's Thump-Thump. only needing 25 explosives to use, and ability to cripple limbs. this for me is my favorite suprise ambush weapon and death claw crippler.
Silenced Sniper Rifle. I end up using it even when I'm not playing a Guns character. Its ability to kill faction-allied NPCs without incurring rep and karma loss is extremely valuable.
I always lug the Anti-Material Rifle around if I play a rifleman character. I just feel more...secure knowing that I can kill most things with one shot from a distance.
Riot Shotgun if I play a shotgun obsessed character. You can take down pretty much any single target with a drum of slugs and the Shotgun Surgeon perk.
Oh wait, you mean in the game. In that case, I carry my modded .45 caliber pistol and the All American with 10 magazines of ammo for each and a couple different types of explosives.
I generally don't leave home without my AMR. It has the range, accuracy and firepower to put down pretty much anything before they can even become a problem.
My current character, though is a pistol/SMG and explosives user. She doesn't leave home without Thump-thump. It's the only rifle-grip weapon she uses. Still debating if she'll use the 12.7mm SMG, though, since it is two-handed.