I have a friend that has incredible bad luck. Her husband spends most of his time in a wheelchair. He can take some steps on flat ground but can't go up a single step on stairs. She herself also has a special disease which puts her into a wheelchair often. She can walk a bit better and can take stairs but only for a short while.
One of the major concens for her was getting her disease recognised. This took several years longer than it should have and even now it's still an issue. Because of that they only received a very low income from our health insurance system. Easy to say, money will always be an issue for them.
At some point I was in a very similar situation as yours where she was complaining about how she couldn't afford certain things. I too didn't know what exactly she expected of me so I just asked her:
When you're complaining about all the crap that happens in your life, do you just want me to listen or would you like that I try help look for solutions?
(Don't know the wording I used exactly since it's been a while a go, but it must've been something like that).
She appreciated me asking and explained that complaining about the crap is just her way of coping with it all. She said she wouldn't even accept any monetary gifts because those would make her feel like she failed in life.
Since then she just complains to me (and my wife) about every crappy thing that happened to her that day. And we confirm that her life sucks most of the time ... and then distract her with cute baby photo's or happy news about a disney weekend we're planning to go with them together or asking about the few awesome things she does experience.
Because I know what she expects of me I can be exactly the friend she needs most. Knowing that makes me feel good when I'm just listening to her complaints even if I have no idea on how to respond to her other than "yeah your life does suck often huh ...".
Just ask them what they expect of you when they're complaining. I wouldn't be surprised of most of the time people just want to vent about their issues for a while.