In the Aussie SAS Kit of Bob Cooper, besides the uses already mentioned the cooled damp tea bag is also applied to burns and scalds as a first aid treatment. Not sure if this is a real medical technique based on the tannins or if it is just an "old wive's tale" being perpetuated. A brew is a great morale booster, not so much the drink, but the time taken to rest and perform the everyday ritual of boiling the kettle/billy/foil cup, especially when performed in a stressed/unusual environment. Then tea becomes a symbol of normalcy, not just a refreshing drink. The time taken to heat the water is valuable time to think your situation through.(Also, noting the diuretic effect, you don't drink tea if your water supply is limited).