NOVA Bomb, because i love my doomsday weapons...There are actually real world counterparts proposed in the Cold War Era. Look up GNOMON and Project SUNDIAL - Gigaton Neutron Bombs as a Concept, Castle Bravo or the Tsar Bomb pale in comparison to these.
All the other Nukes from Shiva to FENRIS/ Fury
Ideal Loadout on the Ground:
Sniper + Dual Smg
Energy Sword + Dual Needler
Bruteshot + Dual Mauler
Needle Rifle
DMR
M6 in Halo 4
Type-50 Concussion Rifle
Special:
T-27 Shade (Fuel Rod Gun in Halo: Reach)
Target Locator to call in Air Strikes (if only you could select the type. Like Bomb Runs, Railgun rounds, Attacks from Longswords or Vultures, etc.)
Missile Pod LAU-65D
M71-Scythe in Sword Base with 20mm HEIAP rounds
Gauß Cannons of all kind
In the Real world:
Barett M107
When 50 cal doesn`t cut it: 20mm Anzio
Kriss Vector ACP
Glock 17 and 19
1911 Pistol
Desert Eagle
AA-12 Shotgun, even better Fostech Origin preferably with explosive Frag-12 Ammo
Hope that small list will suffice
Despite the appearance i am fairly critical of Weapons in normal life though...