What would be a “good” thing for the government to tax?

I’m working on a economics writing question and need a sample draft to help me learn.

What would be a “good” thing for the government to tax? This is a hard  question, so please think about it ? Some things to keep in mind:

Demand for the product can’t be too elastic or people will stop buying the product instead of paying the tax

The government tries to make taxes “fair” – they don’t want them to disproportionately impact people with lower incomes. This is why they don’t tax food at the grocery store, diapers, feminine products, etc.