Anything small enough that I can stomp to death with my boots like insects, little frogs etc.. non flying tiny animals , I could crush them with impunity.
Unless it's something really poisonous , in which case I would preform a tactical retreat , lest it somehow survive my first stomp, then crawl up my leg and kill me with a poison/venum bite.
As for other animals, if it flies then I have no confidence to win bare handed, no matter how small of a bird.
I can kill almost all fish types provided we fight on land. (I would wait for them to suffocate then attack the corpse)
When it comes to land animals, if they're small dogs or cats that I can kick flying then I like my chances. But a medium sized dog then I have to fight for my life and it's not certain if I could win.
Something that alot of people underestemate is the psychological attack that dogs do during a fight. Which is barking so loud they make your ears go numb, it can be very effective if you're not mentally ready. And one moment of hesitation due to shock from the bark , that's all a dog needs to pounce and bite your neck.