When you say self-sufficient, do you mean it as in totally cut off from the world? In some places (like Ireland) monestaries attracted other people to settle nearbye and became hubs of the local economy. There could also be a hostel for sick and weary travellers, or pilgrims to a local holy site.

Also, many (if not most) of Europe's variety of cheeses, wines, and (iirc) beers were invented by monks. Elsewhere in the world, monks invented martial arts and forms of meditation instead. I'm not sure what exactly that says about Europe.