Nicholas likes to be prepared. For instance, what if he is up in the Far Meadow, and he finds a good harvest of acorns but he has no wagon to carry them? That is why his wagon is always bumping along behind him. He says it's worth the extra effort. Plus it is shiny.
Nicholas bear comes wearing picnic overalls and a bonnet. Like all the Hazel Village animal clothes, they are removable so Penelope can change her outfit to her heart's content.