Sex clubs.

We have dozens of unused redundant churches here and they are large imposing stone built buildings unlike the simple wooden structures in the USA. Many have been converted to dwelling houses,clubs, antique stores etc but quite a few are just slowly decaying as it would cost too much to renovate them.

Rent the spaces for other social gatherings

I played in a club in Rockford Illinois that was an old church. It was a great room. You can do anything with them. They are just buildings. I love a lot of church architecture.

In Australia many churches have been sold to the public and they convert them into lovely homes. In the UK I saw a large church having been converted into apartments.

Brothels or dance clubs would work in church buildings, but homeless shelters seem fitting.

I've always wanted an old church to turn into an art center.

I'm going to live in the belfry and throw my trash done in the sanctuary... Oh wait, that's been done already

Some old abandoned churches were converted into luxury flats (apartments) in London over the years. It would be better if the remainder were converted into affordable accommodation for people who currently are unable to get a foothold on the property ladder because of the highly inflated price of property.

I would love to turn a church into an intentional community. All those classrooms for different families as well as congregational and kitchen space for common cooking and activities

Gay bars.

Marijuana dispensaries, and brothels.
I'd invest in both.

I've seen a few well constructed churches I wouldn't mind living in... you know, once all the surfaces are bleached to remove the residual evil...

In the case of American churches, you may as well just demolish them and put the land they stood on to a better use. Over here, where most of our churches are medieval and of considerable historical value, it's slightly more of an issue as most of us agree that while religion is a bit silly it's left us some very pretty buildings. Fortunately, they make good community halls and are ideal for things like youth groups, parties, club meetings and suchlike, so they still earn their keep even if only five or six people show up to cast magic spells on Sunday mornings nowadays.