Sweating is something you absolutely would want to avoid.

Yup, lack of ventilation is the biggest drawback of a bivy bag. Excluding excess sweating (which you try to avoid), there will always be condensation in such a bag. It will make you damp. Given enough time, it may soak your clothes completely.

And since these bags are uninsulated you just can't expect them to be anywhere near warm enough by themselves. It sure is better than without a bag - but if you want comfort you need a sleeping bag and something to insulate yourself from the ground (bough bed or ground sheet). If you want comfort for prolonged periods of time (say, more than a night), you also need a shelter with adequate ventilation and/or something to heat it with (stove or fire). Or make a big honkin' fire in front of a lean-too, but that isn't practical in all circumstances (injured or lack of suitable firewood).

The bag or a perfectly wrapped heat sheet works because

• The excess moisture will not evaporate (major cooling factor, but also a potential long term problem since your clothes will get more and more damp, possibly wet)
• The direct heat transfer from you to the air is delayed (you're warming the air inside the bag, which then heats the bag which then heats the outside air - a much slower process than you heating outside air)
• What about the manufacturers claim that it reflects 80-90% of something mysterious called "body heat" or similar? Sorry folks, the "reflects 80-90% of body heat" is a scam - it reflects 80-90% of your radiation. The reflection part is real, but heat loss due to radiation is not that important, I am guesstimating maybe 5-10% of the total heat loss from a person. If those numbers are reasonable the reflected radiation effect will reduce the over all heat loss by 4% to 9%. Significant, but the two factors above are much more important.

With a bag, you can breathe out through the hole which cuts down a lot on the moisture content. You can also experiment by making some ventilation slots - but it is a very delicate balance. Too much ventilation and you loose too much heat due to evaporation and heat transfer to air. My bag has zippers at 3 edges, so I can experiment with ventilation without cutting holes. With a sealed bag I'd try to ventilate through the main opening, not cutting ventilation slots or anything.

All those things considered, I still prefer to have the option of a bivy bag. That doesn't exclude carrying a heat sheet (which are small multi-purpose items). Trying to make a waterproof cocoon out of a flimsy heat sheet - and make it STAY that way while trying to get some rest, hydration and food - just seems to be too much of a flimsy project for me and my liking.

That being said, neither bags nor sheets will be anywhere near comfortable over the night in a cold climate. But you're much better off inside your cocoon than without one.

Considering all the changes suggested so far, I only have one.

Swap the stick tape for pad tape. It can also be used for First Aid tape, and if colored can work as flag tape.

Granted that toy biners are handy for that purpose, in a survival kit where you are concerned about weight and bulk, I ditch the biners and use an all cord, adjustable lanyard tied with a double fisherman's knot. The DF knot is formed around both sides of the loop, giving you an adjustable figure eight lanyard.

If weight and bulk are concerns, I would definitely ditch a toy biner. The carabiner police are on your case....

As a side note for carabiner use; when I used to do a lot of alpine climbing, one standard method of removing someone from a crevasse, or up a cliff, if they are unable to do so themselves, was the use of a Z line. Essentially, this is just a zig-zag of anchor points, to allow one person to be able to pull someone up via a rope. Its a pulley reduction system. Now, using the "not rated for climbing" ones I do NOT suggest using for person-rescue-but, if you had a few attached to your pack, and needed to, say, move a log, you could rig a Z line up. Again-without proper training & equipment, do NOT attempt to rescue yourself or someone else with this. Failure of the system can potentially result in death!
That being said, the system works-I also used it for high angle rescue on S&R. Again though, we knew what we were doing, and had the proper equipment. With little biners & paracord, you are limited to what you can move-but, it beats throwing your back out, if you need to move something

I'm a little confused as to the purpose of this kit - if it lives in your rucksack then it is a back up to what you already carry, and it's hard to critique without that info. It isn't stand alone

To me a PSK needs to be carried on your person - a rucksack should have all kinds of useful stuff already, the psk is for when things have gone pear-shaped and the rucksack is missing/sinking/on fire/being mauled by a grizzly :-)

Bigreddog - I am 100% with jzmtl on this one. I use my rucksack, daypack or waist pack as an extended outdoors / wilderness PSK because the pocket size kit I've been able to make will improve the odds but are severely lacking in terms of shelter and water procurement. I can cram my bivy bag, water bottle and a pouch that holds the rest (which would be the classical "PSK") into the pockets of my anorak, but the are bulging to the point of discomfort - and where do I then put my gloves / mittens? (Standard procedure: Gloves off => into anorak pockets).

Whenever I'm into the woods or mountains I carry some small pack of a kind. The typical day hike it will hold comfort items, food, snack, whatever... and my "extended PSK" items. A quick jog or skiing trip means a small pack that will contain just those PSK items (this routine is something I started with after being a member here). A camping trip means a bigger pack, with some means to carry the PSK items if I venture out to explore.

If I replace that big heavy bivy bag with an AMK bivy bag (1/3 the weight, probably a similar reduction of volume) I just might come down to a size small enough for pocket wear. Some day I'll probably test that out. In the mean time I make the decision that the risk of me being stuck without my pack is small enough for me to live with.

Quite frankly, I am somewhat allergic to the classical "survival-in-a-tin" kind of PSKs. Some fishing hooks and moisture damaged matches doesn't exactly cover my bases in the shelter department. Don't get me wrong, altoid tins or Doug Ritters PSK pouch is a great way to carry some highly practical multipurpose items. But the bulk within an altoid tin is too small that I can live with that size restriction and call it a PSK.

The purpose of this kit is not something to have on me all the time, rather something that contains the essential items for when I'm outside populated area, so I can just throw it in my backpack without having to pack all the individual items.

I live in a large city/suburban area so most of the items inside isn't useful.

Were you to include some waterless hand cleaner, it would double as a fire starter.

For something labeled "extremely flammable", setting fire to my alcohol based hand sanitizer gel was dead dull boring. Yes, it burns. But it doesn't lit easily and it doesn't burn very hot. I was unable to lit it with a fire steel, I needed open flame from a lighter. It improves quite a bit if you soak some cotton balls - but petroleum jelly cotton balls works a hundred times better.

As always, your mileage may vary, your local brand may be better and so on. Test it before you depend on it.