A useful distinction
Materials are only one part of organising an activity. Space, preparation, administration and communications may also require resources. A fictional example that ignores them can make a project appear easier than its actual plan supports.
Put it into practice
List the work first, then connect resource categories with those tasks. Identify what is donated, estimated or confirmed rather than calling everything free. Use appropriate accounting support for actual classification and reporting; this exercise is a way to discuss scope in plain language.