"put it into your pocket",
Dr Jamshid Ibrahim. In this case, using 'into' makes it sound more serious, like you don't want "it" to be lost or seen by others.
Results 1 - 10 of about 1,260,000 English pages for "put it into".
Results 1 - 10 of about 5,430,000 English pages for "put it in".
Perhaps, that's why a Google search reveals many more instances of 'in' used with 'put'.