I wonder how feasible it would be to construct a community garden for people who live in apartments and/or don't have room for a garden. Maybe that's too big a project for this purpose....but something I think would be good at some point.
I like this idea, too. As Steve pointed out, water might be a problem. If some space could be found somewhere within the city hall/zoo/park area it would be great to set up a rainwater collection garden. The rainwater could be collected from the senior center roof and directed to a cistern located in what looks like empty space alongside the train tracks on Google Maps or to the grass area behind the senior center adjacent to the parking lot. The Stafford Street apartment garden is a good idea, but kind of limits it to those residents. Same with the garden already established at Theodore Judah (which also lends itself to rainwater collection from the covered eating area right next to the garden, but then having strangers come on school grounds during school hours probably not appropriate.) Again, probably more of a project than Steve was looking for.
The only thing I can think of involves sidewalks that need fixing or chunks of asphalt missing from streets and I don't think that can be done by amateurs.
I always thought it might be fun to plant a bunch of daffodils concentrated in one spot like the slopes alongside FHS or an entry road to Folsom from the freeway. They don't require water. Just plant in fall and wait for spring.
I'll keep my eye out for better ideas more in line with painting and cleaning.