Collars only? ... Some dogs LIKE hats!
I don’t throw parties for the animals. But I do buy them gifts (toys, treats), when possible.
I’ve never thrown a party for my personal dogs (altho heck, why not, the dogs would probably have fun since it would involve people giving them attention and food, their favorite things) but the organizations I’ve belonged to hold what amounts to parties that involve dogs. So what, everyone has a good times and often it involves raising money for rescue etc. Our local golden rescue has a big Expo every year. I go to take photos for them. It’s a huge party. Everyone has a great time and they raise money. I recommend it.