If, like me, you are an expatriate living in the US, but you don't have US citizenship yet, there is a good chance that you are *slightly annoyed* (or downright fucking angry as heck) about the current state of affairs in the US. What can we do about it?
As you certainly know, we can't vote in elections. But there are many things that we can do to move the needle.
Can we donate money to political parties and candidates? Yes, if (and only if) you are a permanent resident (i.e. if you have a green card). Then you can donate in the same amounts and limits that a citizen.
And without a green card? You can volunteer your time as much as you want, but you cannot donate any money (or make a donation in kind), or spend any money on behalf of a candidate or political party.
(For instance, you cannot pay for the rental of a venue to hold a rally, but you can host a meeting in your home for free.)
Check transition.fec.gov/pages/brochure… for all the details. (Ctrl-F "green card" for the section about green card holders!)
One of the two parties is relying on massive voter suppression (i.e. preventing people from being able to vote) to win the upcoming election; so if you have *time*, you can heavily influence the election by helping people to vote.
If you don't have time, but have *money*, it's harder to treat the root cause, but you can help by doing some damage control by donating to non-political, non-profit organizations helping those in need.
Personally, I support as I can the following organizations:
ACLU | aclu.org
HRC | hrc.org
SPLC | splcenter.org
ACLU | aclu.org
HRC | hrc.org
SPLC | splcenter.org
If, like me, you are particularly concerned about the recent announcements by the Department of Health and Human Services to dramatically affect the rights of transgender folks, you can also donate to any of these organizations:
(If you weren't aware of these news, I suggest that you check this article: nytimes.com/2018/10/21/us/…)
If that seems pretty abstract to you, one of the consequences (not the only one, but the easiest to grasp) is that they want to prevent transgender people from being protected by Title IX (the federal law that forbids discrimination in education on the basis of sex).
How? By removing the definition of "transgender" from the text and defining sex and gender as the sex at birth. If you can't be transgender (because it doesn't exist in the law) then you can't suffer discrimination for it! 
That's just the tip of the iceberg, though. There are many other consequences, and not just for transgender folks. I'll let you read further if you're interested, and reach your own conclusions.
Let's recap: as an expatriate living in the US, if you're on a green card, you can donate to political parties and candidates. Otherwise, you can't, but you can still volunteer your time, and make (tax-deductible) donations to non-profit organizations that will help your cause.
