You might choose to collect art by and about transfolk, or people with disabilities, or any other group that interests you but rarely appears in public collections. Or if not art, then perhaps literature, music, or some other thing that represents their lived experience and accomplishments.
If you're an artist or other creator, you can contribute by making things that display diversity or focus on less-covered topics. Right now, there's a lack of diversity in art and other creative fields, but that's a problem we can fix. Anyone can contribute to fixing it.
Paint ALL the stories!