Bug Repellent and Ear Plugs are a necessity, but a good portable dop kit goes a long way, especially when you consider the wait you may have if you use the on-site showers at the most popular times (like 6:00-11:00am). My must-haves in this department are as follows:

Dop kit mesh bag:
I use a compact one with plenty of zip compartments and a big loop, so I can hang it on the clothes hook and grab what I need out of it, as I need it.

Camp towel:
Small, super absorbent and again with a loop so you can hang it from the clothes hook. These dry really fast, too.

Hotel size or liquid soaps.
Bring backup... I left my 1 bar in the showers on the first day of West Bend and you'd be surprised at the amount of stares you'll receive to the request "Hey do you have an extra soap on you?"

Flip Flops:
You can walk to and from the showers and it's much better to shower in these than stand barefoot on the floor of a shower stall after it's been used by about 500 prior occupants. YMMV.

Good luck!