First two I'd say to grab would be a Schimdt Rubin K31 and a Russian SKS. (Very nice one for sale here actually
http://www.thehighroad.org/showthread.php?t=273689)
The reason I say one of those first is due to my view that they are starting to disappear. The K31 is getting a bit harder to find compared to maybe 6 months ago, they're known for quality, accuracy, and workmanship.. And a stock that looks like a beaver chewed on it. The Russian SKS is a very nice collectors piece, I've heard they have better quality then the Yugo's and are very solidly built.
Once those are grabbed I'd look for a decent condition Mosin Nagant, there are many variants, you'll need 4 of the 91/30's one hex. You'll need a few of these. 1 round wall Izvehsk, 1 Round wall Tula, 1 Hex reciever Izvehsk, 1 Hex reciever Tula. Then you'll need to start looking into the M44... Did I mention the Mosins are addicting?
You're going to want to look for a decent condition Kar.98 these are starting to be harder to find as well. If you can find a decent, matching, non-scrubbed one for under or around $220 it's a good deal IMO.
Take a look at the civilian marksmanship program. Get the requirements and put in for a Carbine ASAP. These are limited and it's going to be difficult to find them for a decent price once the stocks have run out.
Pistols, look for a decent Nagant Revolver (single action if you can) and a decent German P-38
But these are just my opinions. I, personally, do think of them as collectors pieces, but just the same, I like to shoot them too. I've no use for a gun that won't be fired. My Yugo-M48a, un-issued before I got it, has over 600 rounds through it now. My 91/30 has about 300 through it. I'm praying this weekend is beautiful and my range is done with renovations. I've a 91/30 with PU Scope mount and my new K31 to test fire.
As far as what you "must" have, there's really no right answer. It's all about what you like, what you want, and what you want out of the C&R.