You can staple them but I recommend you don't because they are scanned. Try to keep it organized with paper clips for now. Number all your evidence and label it to the corresponding requirement. So, it is obvious.
__________________
Sent 10/19->WAC accepted 10/24
I-797 arrived 10/27
Biometrics letter arrived 10/29 Biometrics done 11/20
EAD: February 7, 2013 SSN:Already Have 
DL:Gonna take a month or two..haha.never bothered to learn..too scurred