There's a charming old picture of the hoary Universalist church in Oxford, Massachusetts with retail space on its ground floor and the meeting-space above. Wise, that. Empty churches -- by which I mean the buildings -- are bad stewards no matter where or when they are, and these days a bad steward might kill the institution.
Rental income is a one option, but few can have a shop on the first floor. (Community Church, Boston is a conspicuous exception.) Weddings can be a blessing or a curse, depending on staff pressures. I have a hard time imagining meetings providing much money for most churches, and having a renting congregation is fraught with its own conditions. (More about that later.)
Sometimes people talk about a nursery or a school. But all the ancedotal evidence I have for this option makes it seem a poor choice. The school wears the building hard, demand too much of the staff, pay little, but increase the insurance liability and so forth. And besides, it seems to play into the oft-rehearsed delusion -- as does weddings-as-savior -- that church is really for people who grow up, get married, have kids and come back. What is this, the 1950s? (Single and child-free people get the message.)
So what other option is there? I have one in mind, now that I've set up the situation as I see it.