Ask not what Octave can do for you, ask what you can do for Octave!
There are a number of ways that you can contribute to help make Octave a better system. Perhaps the most important way to contribute is to write high-quality code for solving new problems, and to make your code freely available for others to use. For inspiration, we have a wish-list of projects and feature requests.
If you've written a useful function for Octave that you would like to make available for others to use, please post it to the sources mailing list. Messages sent to this list will be seen by the Octave maintainers, and will be considered for inclusion in future releases of Octave. The messages are also archived, so even if the code is not included in a future release, it will remain available for others to use.
If you find Octave useful, consider providing additional funding to continue its development. Even a modest amount of additional funding could make a significant difference in the amount of time that its author can devote to development and support.
If you cannot provide funding or contribute code, you can still help make Octave better and more reliable by reporting any bugs you find and by offering suggestions for ways to improve Octave.