I donate to this and that charity during the year, all over the place really lol.
But there are lots of things to do that help out animals that don't cost money as well. Try going to your local SPCA/private shelter/pound and taking a few of their dogs for a walk. It can take less than a couple hours, if that and you help out both the shelter and the dogs.
There are also lots of websites that let you click each day to donate money. Sure it might not be alot but if tons of people are clicking each day and you do it year round, it can add up.