Batman is never without a sidekick/Robin because he is pedobear.

Spiderman has never officially had a sidekick although he let Frog Boy hang with him for a while.

Superman has his faithful dog Krypto.

The Hulk had Rick Jones as a sidekick for years.

Captain SODa gave up heroics to manage a Burger King and doesn’t need one.

Captain America had Bucky the Boy Wonder who died and for many years was the only comic book character to die that actually stayed dead. But then some lame writer brought him back.