I'm guessing here, but some dogs are trained to fetch (I don't mean "Fetch, boy!" but pick up things and hand them over), open doors, etc.

Quoting from Dogs for the Disabled: "For the adults with physical disabilities we help, each dog can offer practical support with tasks that many of us take for granted, for example, opening and closing doors, helping people undress, and even emptying the washing machine."

Here's an article about the basic training (before they're assigned to specific people training): "Avon learnt to retrieve to hand any article presented to him including remote controls, keys and purses, to pull open doors and drawers, and pull zips, gloves and socks. He especially loved pushing buttons including pedestrian crossings and door buttons at the bank! Vicky also worked on Avon’s heel work and handler awareness, recall, and got him used to walking alongside a wheelchair."

There's a book for disabled people who want to do some of their own training: Teamwork II: A Dog Training Manual for People with Disabilities: "This edition of TEAMWORK II which as been revised and expanded, teaches the service exercises, such as retrieving dropped objects, turning on lights, pulling a wheelchair, etc."

(Sorry, I guess I went on a bit longer than I meant to.)