"You never had none, you crazy bastard. I got both of 'em here. Think I'd let you carry your own work card?"
Chapter Four (page 75)
"...Just come to look at my puppy. And I seen your light."
Chapter 6 (page 113)
"I done another bad thing."
"It don't make no difference,"
When George took Lennie's work card it showed that he cared for him and wanted them to be able to work together. He knew that if Lennie had his own work card, he would likely loose it. So, he was willing to take responsibility for it to ensure that they both are able to work.
When Lennie came into Crooks' room, he mentioned that he had just come from the barn to look at his puppy. This shows that Lennie is excited to get his new puppy and is willing to take responsibility for it and make sure it is safe.
When Lennie admitted to George that he had did a bad thing, it showed that he knew he had done something wrong and was willing to take responsibility for his actions and except his punishment.