You can offer to sponsor an animal by donating a small amount of money each month.
Spread the word about adoption vs. buying from breeders.
Raffle off something pet-related and donate the proceeds to them.
Ask everyone you know for “Christmas presents” for the shelter.
Encourage people to donate, perhaps instead of buying you one present they intended to, they could donate the cost to the shelter.
Visit the director and offer to help with paperwork, adoption screenings, addressing envelopes, or whatever else needs to be done.
Report animal cruelty and neglect immediately instead of letting the problem worsen, and encourage others to do the same.
Ask what supplies they need and then get together with your class or coworkers to send a box full of their preferred type of toys/food dishes/etc.
Get together a group to bring the office workers hot chocolate and sing them carols during a lull between visitors. Hand out Christmas cards with animal pictures that say something like ‘You’re the real Santa Paws’, etc.
Adopt a pet if you can.