For the past three years, my daughter has asked her party-goers to bring a donation of needed items for the all-volunteer cat-rescue network where we found our sweet kitty cat. We send guests the link to the page that lists the organization's greatest needs, and the kids show up with gift bags of cat toys, cat food, cat litter, and the more prosaic needs - paper towels, trash bags, and postage stamps.
Some people choose to give money to the agency, but most come laden down with wonderful piles of cat stuff. So they get the fun of picking something out and dressing it up pretty, and my daughter gets the fun of seeing what people brought, and the organization gets lots of supplies for its foster families.
It feels festive and virtuous at the same time, and we don't add to our clutter. And the agency is soooo appreciative of the fact that we use their list and people buy what they need, and my daughter gets a lot of love for "giving up" her birthday presents for the kitties.