Tony - 

One of his t-shirts which is huge on you and really soft and cuddly

Steve -

His Captain America outfit which drowns you

Clint -

His leather jacket to show that he is yours and you are his

Bruce -

One of his long sleeved shirts because you didn't like your arms being on show

Thor -

His cape as you could wrap it round you or run with it flying behind you

Loki -

His helmet which didn't fit but you wore it to imitate him badly