Hi Hector,
It definitely is possible! Before I (and others) start listing projects, I'd like to point out that fixing bugs is another way of contributing to Sage that you may not have considered. That can be easier than writing new code, because you don't have to come up with the major ideas or do a lot of writing. But you do have to figure out how the code works, how it doesn't, and how to fix it. A few problems have come up already on this site (e.g. with numerical integration, or colormaps for certain 3d plots), and there are a good number of further bugs mentioned on the Trac site.
By doing this, you also get experience with a lot of Sage code and hence will have an easier time writing quality code when you need to do so.
(Note that this is my particular opinion, and I'm not a major contributor to Sage. I suspect there may be others who agree, but also a fair number who disagree--they can go ahead and vote this answer down!)
"scripts" used to have pejorative connotation vs. compiled programs; but now that many languages are hybrid (both interpreted and compiled), just "programs" is sufficient terminology IMHO.