I have a good old friend who fronts a popular copy band. He doen't bring his full kit around anymore(unless he's playin in The Village with his original band). Just a set of bongos and stuff.
Babaloo!
He sings lead vocals too, and keeps an assortment of small hand percussion stuff in front of him on the stage.
Some stuff gets passed out to the audience, and they vibe all night to pop stuff, old and new.

I'd say anything you can tap or shake or bang on is fair game for an "unplugged" gig.

When I worked in the city, I used to pass street percussion ensembles jamming on upsidedown empty joint compound buckets. Playing was intense. Sound was enormous. And the intruments cost them zero dollars.
:p:

The best known street drummer (and all-around looney) in Toronto was using nothing but buckets last time I saw him... handy, 'cause he sat on one, put out two for change and played on the rest. Somewhere someone published a photo of him riding his bike to/from busking, with 7 or 8 buckets stacked up on the handlebars. Graeme Kirkland....

On an acoustic gig I've found that a DST style mountable tambourine setup on a Gajate foot pedal bracket is the most useful thing possible. The minute you remove drums and just play 2 and 4 with your foot on that tambourine, it's Unplugged City. The vertical mounting of the tamb alows for maximum 'ching' time from the jingles too...