Yeah, unfortunately the way the avatars are right now, you can only equip certain items at a time. :c
Although sometime in the far off future, when Diana and I finish the site and begin revamping it, we're probably going to do a big layer change up, to make room for multiple items of the same category to be equipped, etc. Or more categories. But don't hold your breath! Because we have to actually finish the site and work on many other things, first.