I mean in metal tin, where does not has many space...

no way to fit the space blanket / poncho / trash bag in.
It has to be carried outside (wrapped outside the tin) seperately.
OR
get a bigger tin / bag / container
Don't limit yourself to the altoids tin.

<img src="/images/graemlins/grin.gif" alt="" />

I do know of a space emergency blanket that would fit in a tin, but I don't use it. Best to carry a plastic survival bag or poncho seperatly.
It you only need the shelter, you don't have to open the survival tin, and you can better use the space in a tin for other items.

should? Well thats your dicision. I don't know anybody with a space blanket in a PSK. But that doesn't mean it's "wrong".

A space blanket or other forms of shelter are likely to deployed when you are freezing your six off, so quick acces is a factor that has to be taken in account, so are space issue's.

Appropriate clothing for the weather is probably the most critical item of all. PSKs are tough to carry running nekkid through the woods. A well folded poncho or small tarp is easilly carried in a large pocket. My Filson Packer coat always shocks people. From the doubled game pocket in the back I can produce a 9'x9' sil tarp. My twin PSKs ( one is dedicated solely to medical items) ride in the two front pockets along with a water flask and survival food ( fruitcake, chocolate and tea.) Theres also a pair of Dachstein mittens and a balaclava in there. The sheepskin shawl collar always draws attention on trail or town, where people in California virtually walk around in pajamas or half nekkid anyway <img src="/images/graemlins/grin.gif" alt="" />

I carry an Adventure Medical Kits survival blanket in my PSK.
My reasoning is that some form of rapid shelter is the second most important thing you can carry besides fire starting equipment, especially here in Montana. In 4 years of being a member of SAR I have seen people die from hypothermia that shouldn't have.
Remember your rule of 3's
3 minutes w/o air
3 hours w/o warmth
3 days w/o water
3 weeks w/o food