It's difficult to incorporate volunteering into travel you are doing for business because more organizations don't have the capacity to involve volunteers that aren't from the area. And drop-in-anytime volunteering is rare.

Most beach cleanups and trail cleanups allow you to pre-register, and you don't have to be from the area, so if you do some research before you are in an area and see if you can find that, you can sign up.

You can certainly arrange travel volunteering, like through HistoriCorps, which mobilizes volunteers to restore historic sites on public lands. State Departments of Fish and Wildlife often have volunteering weekends, where volunteers camp and spend their days restoring habitat or counting wildlife or releasing fish.

Such opportunities are noted on r/volunteer sometimes.