Where are you going? If only a short walk from the car, is there any chance you may become lost? This is a realistic question.

In the mountains, the clouds roll in. Because you are at the altitude of the clouds, you can get enveloped in "fog". In low lying areas, fog may roll in. Enveloped in a dense fog, most experienced outdoorsmen would be at risk. How much risk, depends on how much preparation and what appropriate clothing and appropriate outdoor gear you have with you.

The most basic shelter, in my opinion, is a foil 3 oz Adventure Medical Kits, emergency sleeping bag. Out of wind, with layers of clothing, it is possible to avoid conductive heat loss.

There is survival, by sleeping near the base of thick brush, curled up, knees to chest, hands tucked in. But we can do better. I don't want a miserable night, and neither do you. Reduce risk, by having more shelter than some thicket of underbrush.

Any outdoorsman, or woman, would benefit from providing for having to remain out overnight. This lessens the panic. You are prepared: there is no running in large circles. Even experienced hunters are found dead, after exhaustion from running in panic. If you know you will be alright overnight, there isn't much reason for panic.

What lightweight small volume shelter, that may be carried in an ordinary waistpack, will do the job?

I have experience wrapped up in all the clothing I had in a ToddTex bivy, in the cold and wet mountains of coastal southern Oregon. The ToddTex was not cold to the touch, nor stiff. I was comfortable. I slept well. I recommend an alpaca wrap wrapped around the body core and a bivy fabricated of ToddTex material, for damp and cold conditions or have a quality synthetic sleeping bag rated for the lowest anticipated temperature and a ToddTex bivy.

For a 10 Essentials light duty rucksack or waistpack to be either lightweight or ultralightweight and have a reasonably compressible compact volume might include, for example, a 19.6 oz Bozeman Mountain Works UL 180 Quilt and Integral Designs Penguin Reflexion bivy at 23 oz with reasonable insulation from the ground from a 3/4 length closed cell sleeping pad or "forest duff" may be your choice.

I can also recommend an open design tarp of catenary-cut for practical lightweight or ultralightweight shelter, that can be set up to stand up to ordinary windy conditions you may expect to encounter and may be opened up to reflect a warming fire, if necessary.

Many of the shelters I have listed can be open to fresh air or closed down to the ground to retain warmth and still have reasonable interior height for changing clothing, yet, are lightweight and even ultralightweight shelter.

There is, for example, the reasonably lightweight 28 oz MSR Twin Sisters tarp shelter and the 30.3 oz Terra Nova Laser Competition double-wall tent. The Twin Peaks, now called the Twin Sisters, may be pitched open or closed down. The double-wall Laser Competition is a long-standing successful design.

Most modern tents have a rainfly that may close down to the ground to achieve the benefits of a double-wall tent and offer the option of putting up either the rainfly or the tent or both rainfly and tent. Few achieve this weight: pitch the rainfly.

I have additional shelter alternatives including hammock shelter systems, not limited to the tropics, for consideration at Products: gear.

Make your choice among the many lightweight options available today.

May I suggest you make the initial comparisons online?