An FPS you say.... Are RPG weapons allowed? because if so...
Weapon: A partially sentient shape shifting Blade that takes the life force of my enemies and heals me with it whenever I get injured... I rather like my "I Win" button
Snack: The aforementioned Life Force.
If not...
Weapon of Choice: Revolver. With Scope. And a Knife of some sort, should anyone get close enough to be.... Unpleasant.
Weapon of Practicality: Some manner of Assault Rifle. With Mods.
The Unlikely weapon: The Sniper Rifle from 'Bulletstorm' With some manner of Melee weapon In case I miss.
Snack: *Shrugs* idk, Doritos or something?