Red, I cannot tell you how much you remind me of myself right now. I felt the exact. Same. Way. For the longest time I wanted to help my favorite community in any way posible, but I couldn't donate. I opt'd in to ads, which made me feel better for one which you have already done. That alone makes a significant difference. The more people who opt in and see those ads, the more support the forums receive.
Although I did manage to donate later, one of my favorite ways of contributing to this forum is reporting. I report threads and/or posts for the moderators and they appreciate it a lot. It makes their job easier and sometimes you catch things they miss. It feels great knowing you're helping when things like that happen.
Finally, if you really want to contribute just enjoy the community, make friends, and show the staff you care! My staff theme project was one way I chose to show that I highly respect the staff and appreciate what they have done for our community. I'm sure you can think of a way to show your care, whether it be through talent, involvement or helping around.
Honestly you would be surprised how big of an impact the little things can have.