You can not take anything onto the Mummy. There are lockers available outside the entrance (the first hour is free). You go up to a rental station and place your index finger on a scanner. The computer reads your fingerprint and a locker is assigned to you. When you come to get your things, just go back to the rental station, place your finger on the scanner, type in your locker number and VOILA...the locker opens.
If you are not sure you will make it to Universal Studios, I would wait on tickets.