It is not a bad idea to have something to carry to the shower. During Indoc PC's have so little time to even shower.
Good luck....you will enjoy the experience...my son will be one of the DI's for the upcoming Plebe class.
During Indoc he really doesn't need any carrier for the shower. All he will take there is his towel and soap/shampoo and the bathrobes have pockets. After Indoc alot of the girls will choose to buy one of those little plastic carriers as they tend to stockpile shower stuff like it's going out of style. I never really saw any guys with any carrier.
There are sinks in the rooms so you don't need to take toothpaste and stuff like that to the other bathroom/shower.