I celebrate in a different way. I home cook for him his favorite meals the whole day. I'll take the day off work, and just do things he likes all day. Hiking, fetch, I'll set up an obstacle course in the backyard. Sometimes I'll buy him a slice of dog cake, which he won't even try.
I don't do presents since I don't want him to learn it's ok to rip paper. He doesn't understand presents or need things like clothes or more toys. He has a drawer full of clothes he hardly uses.