Clinton’s policies once elected are the lesser of my worries since unless there’s a massive change in the Congress, nothing’s going to happen for four years if she’s elected besides show trials, more investigations of Benghazi, and impeachment attempts.
Something you can do is support the NRDC, ACLU, Union of Concerned Scientists, NAACP, GLAAD, Brady, or whatever groups have a good track record of using donations to do work you believe in. There are a lot of good organizations out there, find the ones with a decent track record and some influence and help them spend time pressing Congress/the WH on the issues.
As others have said researching the down-ticket elections and making sure you’re voting well there really matters. State/local politicians bubble up to higher offices, so getting decent left candidates into the system is crucial for a future that’s not more of the garbage we’re suffering through now. Donating time/energy locally’s also a way to have a lot more influence if you can do it.