Started contributing to Mastodon development on Patreon a while back https://www.patreon.com/mastodon

I'm contributing because there are a LOT of features on Mastodon's roadmap (https://joinmastodon.org/roadmap) that I'd like to see happen, I use Mastodon a lot, and I can afford to.

they also have merch: https://freshstore.co/collections/mastodon