I think one special act of giving without expecting anything in return is listening to someone. Like genuinely listen to them; their thoughts, ideas, successes, difficulties; anything they are talking about because they trusted you enough to tell you those things.
It may be a huge deal for some people out there to open up to other people, even for the smallest things. I listen more than I talk usually when I meet someone new because I've learned that most people don't give a shit about what you say; they will forget whatever you told them within seconds. They're always waiting for you to stop talking before they start talking about what happened to THEM, what THEY did last weekend, what great thing happened at THEIR workplace, etc.
So, genuinely listening to someone is something most people aren't good at and, in my opinion, being a good listener is an excellent gift you can give to someone without expecting anything in return.