How to Backup when Samsung G S3 not booting stuck at Samsung logo?
I used my S3 in "Android System Recovery" 

The option "WIPE DATA/FACTORY RESET" seems to npt wipe /sdcard/ partition. 

in my case it resolved the isue, now the phone is not stuck, and all the apps that were deleted are re-installed from the cloud by Android because I had backup them on the cloud.

Just as a side note, before  I used the above option to get rid of boot stuck on samasung logo, I couldn't use ODIN to install an original firmware downloaded from here:
http://www.sammobile.com/firmwares/3/?download=14509