1. Buy from community members
Open source communities are typically composed of many of the people whose business interests most depend on the sale of services and extensions of the project. They are trainers, contract developers, support companies, integrators, and more. The very best way most of us can support open source is by trading with those people and businesses.
When you buy training or service-level agreements or contract development, check to see if your supplier is an active community member. Ask them about their commits to the project, their attendance at community conferences, their participation in governance.
Some communities even have a way for members to prove their participation, such as official membership or even certification. There are a surprising number of companies — especially offering level 1 and 2 support services — that don’t meaningfully participate in the community. In many ways, those companies are the real freeloaders and it’s better not to encourage their existence.