Don't overlook the tried and true, low tech implements for indicating your position - signal mirror by day, bright light or fire by night. In SAR situations, even when in radio communication with a helo, both mirror and fire have been very helpful. Practically speaking, everyone has a cell phone these days, and most of the time, they are in communication (not always!). Nowadays many SARs are initiated by a cell phone from the accident scene.

Even just standing in an open spot and waving your arms will be a big help.