How about calling your local Humane society and volunteering your services for a future fund raiser. The humane society is a haven and adoption center for animals ran entirely by volunteers and funded entirely through fund raising and donation. They often have various fund raisers to keep the facilities going.
We all know the street fair /art fair artist who charges for caricatures. I love them :)Why not offer to provide caricatures sketches of peoples pets, or people with their pets if they wish, who attend the fund raiser as many of the events involve bring ones pets along. The money raised minus your supply cost if you wish goes to the shelter. You could also offer to do this with newly adopted pets with a little intelligent negotiation. While doing the sketches free for your time and your art as the money is donated to the Human Society be sure to sign your work and have business cards to pass out with the sketch to promote yourself in the process of helping fund an amazing agency.
Are you lyrical, musical, or poetic?.....do you like animals?
Why not consider the above idea... except make improvisational jingles cheaply recorded on site or hand written improvisational poetry about each pet. This would take more on the spot wit on your behalf but you can use the same promotion as above. If your a musician burn cheep demo tapes or disks with a song or so and information where to hear more to give away with your jingle about the pet. If your a poet and you have a web page or another project that you can afford to give out with your poem do so.
Are you a hobbiest, craftsmaker, sewer, quilter, sculpture, ceramicist, woodworker etc......do you like animals?
Consider the above but rather than a caricature on the spot production create animal centered works and offer to vend a table of your art free or at reduced rate (ie keeping half for you half to the Human Society) of every item you sell at the fund raiser or as fund raiser prizes/ or auction pieces. Be sure to claim your pieces and provide any extra info like business cards with contact info that you deem needed