I just bought a nice human first aid kit that includes the rest of what I want but haven't yet got in my gear (trauma shears! So excited!). I never use a first aid kit as it is sold. There's always stuff that I don't want, and they're always missing something that I do value.

Now that I have a dog (got her a month ago tomorrow!), I basically plan to add some vet wrap (Which is also useful for humans!), styptic powder, and a "FOR HUMAN USE ONLY!" warning label on the ibuprofen (I don't carry acetaminophen; it upsets my stomach) and possibly the aspirin.

The biggest thing is that you have to know how to use whatever you have. I'd rather have more knowledge and less equipment any day...
That goes for a human-only kit, or a human/animal kit.