Having been vegan for two decades, I have created and managed a number of vegan projects and events, given talks and written articles (as well as contributing to various third-party vegan initiatives).
With a similar amount of professional experience, I have also provided free advice to not-for-profit organisations and small businesses.
While free to the respective beneficiaries, these all have a cost to provide (whether in time only, or financially as well). And while such costs are often small, they quickly add up.
So, if you would like to support initiatives such as free vegan events and free professional advice (particularly if you have benefited directly) you might like to consider leaving a "tip".