Surely the best way to survive is to already be in the military and therefore you'll be stationed at a base?
Not really, because armed to the teeth as you are you're going to be the first in to assist evacuation protocols meaning being stuck in the cities aka zombie flashpans.
Remember most infantry wont be carrying north of 300 rounds (less if your not tooling up for a firefight, which you wont be) so in a city of thousands of people even if you're some pro sniper your not going to be able to fight your way out.
Ironically the best weapon for the zombie apocalypse imo would be the humble ruger 10/22 with subsonic ammo and a good suppressor. Light and easy carried, accurate enough to make headshots and thatll do for zombies, plus carrying a couple of thousand rounds in a backpack is a realistic undertaking. Plus in the uk itd be the biggest chance of finding ammo for it as its a very common round.
Combine with a sawnoff shotgun for hairy moments and dealing with humans.
Assuming we're not dealing with wwz zombies then holing up in a castle is by far the best bet, anything designed to keep a determined army with seige artillery at bay isnt going to sweat with a few zombies clawing at the door nor any grouchy survivor bandits, you'd need to be careful who you let in and supoorted but raiding local food and moving towards sustainable farming is going to be a good strategy.