KB's don't take much space. For that matter a good power rack set up has a relatively small footprint too, but then you have neighbors to worry about, and depending on the apartment space is always a premium. Trust me, having moved from a 700-ish square foot apartment in CT to my garage that is probably a good 500 square feet... I know how good it feels to be able to spread out.

I ahve had the debate with a friend a couple times about what I would buy if space was limited... and I'm talking about what would fit in the trunk of my car limited.

I came up with a list like this:
Kettle bells
Sand bags
1 1/2" manilla rope (18-20')
Old car tire with a u-bolt driven through it so you could pull it as a sled

...yeah, that would probably be my top four. With a little ingenuity I could develop a crap ton of training that would hit strength and conditioning.