Make a center console for the thing. I was gonna do that, and have done it for a few vans in the past. You can probably get away with half a sheet of plywood for it since the seats don't sit that high. I know they make one that Wal-Mart sells for $40, but I've found those just don't sit high enough. You could probably make something that angles up in the back that would hold a small bathroom-sized trash can (like one that uses plastic grocery bags, that size trash can). If you built one, you could also run some ducting through the bottom to funnel heat to the back if you use it in wintertime with the church group.
There's also some storage compartments I've seen plans for that are for the back of a truck bed. IIRC, it'd use about 3 sheets of plywood and give you two levels. Since I don't think there's attachment points for a third seat, the whole back end is just open for storage. This would let you add bins on both sides, an open area between them, and then a plywood sheet atop that for the second level. If you want a scan of the article, let me know and I'll see if I can hunt it up for you.
I was also considering hitting up J.C. Whitney for an overhead compartment thingamabob like in newer trucks. I can't remember the cost on 'em, but I know they make 'em for that model year, I just don't know how they attach. See a '98+ Sierra for what I'm talking about.