It is like a piggy bank thing.  You can either do it on an individual or family basis, or or a community basis

 

Just devote a donation box such as an old smarties tube, and keep making donations every now and then when you come across an unspent coin in your pocket.

 

Ideal tip - Buy the smartie tubes for your group of church and let adults and children take them on the basis that they will fill them up, you can get around £12 of 20p pieces in a tube.