This is a great activity to have your students complete in small groups at the end of an economics unit as it has students work together to come up with a budget for how their government is going to spend tax revenue on public services. This activity also ties math in because students have to keep track of their spending.
Additional activity: Have students make campaign posters for the public service that they feel needs more money than the government budgeted for it.
When I did this activity with my third graders, it was really neat to see them work together and come to agreements about how much money would go to specific services--some groups voted while others made compromises. My students got pretty passionate about certain services and the funds that that service needed. I asked them to give reasons for why certain public services needed more money, and they came up with some good answers, like "last year, there were a lot of fires and not enough fire trucks, so the fire department needs more trucks this year." Their campaign signs were so cute, too--one said, "GIVE TEACHERS MORE MONEY!" (such smart kids :)).