I've been struggling trying to fill all 12 spots as well.
1) Ruger 10/22- if I have only one gun, this is it. Easy to maintain, cheap to shoot, extremely reliable, easy to modify, tons of aftermarket parts.
2) Mossberg 500, 12 gauge- I currently use a Mossberg 535 for my hunting needs because the 535 allows the use of 3 1/2" shells. I have the smooth bore longer bird barrel as well as a rifled slug barrel with scope, but love the available barrels for the 500 series- even the black powder barrel which just makes the shotgun extremely versatile
3) SKS (any country of origin) I have owned probably 20+ SKS's and have never had a bad one. My favorite (and most will hate this) is the chinese norinco's. The reason? Because the local pawn shops sell them for $160-$200. They suck for holding their value, but have never had one fail. I also prefer the standard 10 round magazine and the use of stripper clips. Not only is it lighter to carry more ammo vs the hi-cap magazines, they take up less space to carry to same amount of ammo, they are cheaper than magazines, they can be reused like magazines, and if you practice, you can load them ALMOST as quick as changing magazines. Another reason i prefer the stripper clips, once you have loaded the clip, you can toss it away, no worries. Magazines, you have to keep on you and reload them later. You can also buy ammo, preloaded on stripper clips for a few cents more per round.
4) AR15- This is one weapon I have never owned and do not like. I am not a fan of the .223 round, I absolutely hate the entire AR platform, BUT, for Z-day and survival needs, there are tons of people who love the AR and that means ammo will be readily available. For this reason alone, the AR made the list, but it might get booted for #5.
5) Ruger Mini-14- Like I said, not a fan of the AR platform, so the mini 14 might be a good choice. It still uses the .223 round. I havent done enough research to see if it will also use the 5.56 round. I know that a 5.56 weapon will shoot the .223 but do not think a .223 weapon will shoot a 5.56- I could be wrong there.
6) Ruger Mini 30- Reliability of Ruger chambered in my favorite round, the 7.62x39mm. No explanations needed.
7) Marlin camp 9/ hi-point 995/ keltec sub2000- or the reasons stated above by whynot. I added the sub2000 to the list mainly because of the fact it will fold in half and store in a small area not larger than a standard laptop bag. I have also emailed Keltec's R&D department and asked them to work on a 45acp version using Springfield XD mags. They responded that they would look into it, but dont hold your breath.
8) Marlin 30/30 lever action- This is currently one of my deer rifles and again like whynot said, ammo is plentiful, and the weapon is a good brush gun.
9) AR10- As much as I hate the AR platform, you just cant argue against the aftermarket accessories for the platform. Chambered in the .308, lots of power, and tons of accessories.
10) Mosin Nangant 91 30- Another surplus military rifle. We can buy them locally for under $120 still covered in cosmoline. A powerful 7.62x54r round + cheap gun = zombie killing fun.
11) Springfield M1A fully loaded- 7.62 NATO round (7.62x51mm or .308)- This gun has been on my wish list for a while so its one of my fantasy guns. If I ever get $2000 that I have no use for, this will be my first purchase.
12) My last fantasy gun is a standard military issue M-16, that my dad used in Vietnam. For my fantasy gun, I want the actual rifle he carried.
