Glenryck Pilchards are tasty and very good source of inexpensive high protein survival food.

http://www.glenryck.co.uk/pages/pilchards.htm

You can get 3 tins of Pilchards (425grams net weight 485kcal 4.3 percent fat) to a cost of a single tin of Spam (340g net weight 983kcal 24.5 percent fat). If you want to increase the fat content you can drizzle some virgin olive oil over the pilchards. You really wouldn't want to drizzle olive oil over Spam.