Unless you're part of a uniformed military group with medics and an ability to medevac you, a sucking chest wound is probably Mother Nature's way of removing you from the gene pool. Body armor is cheap and readily available to civilians. Edit to add: Emergency medical technician training is also inexpensive and often available as a night class. An occlusive (non-permeable to air) bandage taped on three sides allows you to breathe in but lets air out when you exhale. Think plastic. Sterile is better, and there are commercial pre-packaged options out there. If you have nothing plastic at hand, and no tape, clamp your hand down on the wound when you breathe in, and take it off when you breathe out. (Not criticizing your comment, just pushing preparedness.)