Chest seals are handy things to have for penetrating chest injuries...which causes the lung inside the chest cavity to collapse, resulting in no air exchange. Penetrating chest injuries (sometimes called sucking chest wounds) can happen from almost anything, a gunshot wound, a stabbing, industrial accidents and shrapnel from any sort of explosion.
Treatment is simple: Cover the holes in the chest with an occlusive (airtight) dressing, and secure it to the skin. Check for entry and exit wounds, front and back.
There are purpose-made devices for this, the Asherman chest seal, the Halo seal, the Bolin....http://www.chinookmed.com/cgi-bin/category/s-thoracic_airway
Prior to these devices being invented (in the last 20 years or less) the treatment was to use vaseline impregnated gauze (petrolateum gauze, etc). Conventional wisdom was to peel open the foil pouch and use it, throwing away the gauze.... then tape it down well. Various schemes exist advocating taping three corners, leaving a 'valve' for escaping air...just be prepared to remove anything you put on a patient, if the patients condition suddenly deteriorates faster.
But what if you don't have a purpose-built chest seal, or even petrolateum gauze?
Any sort of airtight material will do. Aluminum foil, saran wrap, a plastic bag.
You could even use the plastic, adhesive pouches that FEDEX and UPS provide (free) to put the shipping documents in for your packages....they stick (as well as most), they're big enough, and they may be available.
Something to think about.