So far we have used the following ones:
Agriculture. Our main revenue source in most sagas.
Exploit a forest. Both for its wood and trapping animals for their fur. Used in 2 sagas so far. Allows you to “carve your own domain” out of the wild, so the feudal obligations of the covenant are few and far between.
Fishing. A village near the covenant specialized in catching some varieties of difficult fish to catch with some help from magic.
Trade. One of our major source of primary or secondary income since a few years ago. Magi are A LOT into sea trade. Easy to make small minor items that help the ships sail better and the merchants get better deals. Can be used to bring stories and run adventures in far away lands without stretching the suspension of disbelief of the troupe.
Create wealth from scratch. Silver, gold, gems and salt have been used so far.
Mining. Silver and tin as well as sulphur. Used in several sagas. “Stone mining” (cannot remember the word in English right now: create stones for building stuff) has also been used. Silver mining was the first income source we got in any of our sagas.
Taverns. A group of several taverns used to get wealth in a urban saga.
Animal training. One of our sagas has the covenant build up a trade for horses that withstood the Gift. Our 6 animal handlers were marked by magic (magical air flaw), and so the horses hated it, but learned to trust Gifted characters. Our war steeds and palfreys were highly prized in the order of hermes.
Selling minor items has also been used, but only on a case by case basis, and more for favors and concessions than as a regular source of income. Selling books and getting moeny from other supernatural services and products as well
Generally we do not like a lot micromanagement, so we simply say that things give enough revenue for X level of development. If we decide that we want more (moving from spring to summer, for example, and needing cash for better labs and infrastructure), we build 1-3 adventures around that theme and go for it.