I'm using the AntAgonizer Armor for fun now
Usually I look into the territory I plan to march through and take weapons with me that would make a good addition. I got my home in Megaton so I usually take it from there. In the south are more Rad Scorpions while in the north are more Mirelurks and Molerats. Raiders are nearly everywhere but Super Mutants for example are only in special places or the Downtown D.C. Ruins. I never saw one roaming around. I take these territorial behaviors of my enemies to plan my routes and weaponry.
Minigun, Flamer - Raider, Mercs, Feral Ghouls
10mm Submachinegun, Power Fist - Animals (Radscorpions, Mirelurks, Hounds)
Hunting Rifle, Shotgun, Rock-It, Power Fist - Super Mutants
Pulse 'Nades 'n Mines - Bots of course!
If I have no idea what to expect I usually take the Hunting Rifle, loads of 'nadies and mines along with the Rock-It Launcher and my Power Fist. I'm quiet handy with the Power Fist and you can make small Minefields if you have to make a quick escape. I got plenty of ammo for the Hunting Rifle and it has a good accuracy so I can deal with tough enemies by aiming for vital parts and it's not that bad to fail one or two shots. Every failed shot with .203 hurts badly you know (I'm really really short on that one. Got like 40 Rounds). If something tough appears you can cripple it with the Hunting Rifle to slow it down and bomb it back to it's mother with the Grenades. For everything else there is the Rock-It Launcher just because it has unlimited Ammo. You're fighting on the world's biggest Junkyard of all times and Junk is your ammo. Seriously, if you run out of ammo with the Rock-It Launcher you have to be blind...