• Each parent should become aware of the estimated amount of child support the state would order with a given custody arrangement and each parent's income. It's possible to include that amount (or any other agreed amount) in the parenting plan. Discuss this with a family law attorney, to ensure you use proper language for your state and to be sure you understand the implications of stipulating to a child support amount.
  
  
• Some states have additional support for childcare expenses. Again, consult with a family law attorney in your state.

• Generally, each home is expected to provide for the basic living needs of each child. That includes clothes, toys, foods, personal care, etc. Child support is intended to help the supported parent provide all this.
  
  
• Other expenses may include extracurricular activities, school tuition, health insurance, unreimbursed medical costs, orthodontics, etc. Consider specifying how those expenses are handled, to avoid future argument.

NOTE: I've found what I consider to be two very good sources for high-quality parenting plans. One offers a set of downloadable plans that you can modify, the other lets you create a parenting plan online and modify it.

• Downloadable Parenting Plans
• Online Parenting Plan Generator