This has probably been said, but try to do all your MSUSA shopping after the park closes. They usually keep the shops open for another hour or so, so do it then instead of wasting park time.
Also, even if the wait is minimal, FASTPASS the Mickey Town Square Theater character greeting. It's not "connected" to the system meaning you can immediately obtain another FASTPASS after getting one for the meet 'n' greet. It may not save you a lot of time, but it will save you some time.