What type of sails and fasteners (in lack of a better word) would be cheap, reliable and easy to use for sail assist or emergency propulsion?
The most likely use of emergency sail propulsion would probably come from a dirty fuel tank contaminating the last set of fuel filters.
In that case REAL sailing ability is required , so what is common for the sail area chosen on an sailboat would be needed.
If the ability to go to windward was not required , the old square sail type spar could be hoisted , and you would blow downwind at a higher speed. Probably 35 deg P or S of dead downwind could be steered.
To beat off the proverbial Lee Shore , a genuine large and robust sail rig is required.