What can I do with them?

Items in the "roleplay" section of the shop are meant to inspire you to develop a character.  They give both ideas and justification for the things that you describe your character doing in chat.  For instance, saying you crash a zeppelin onto the Gazebo of Equilibrium is going to be dismissed by the other players as ridiculous, but if you say "*covers his head with a handkerchief.*" or "*tickles him with her blue parrot feather.*" these things will be believable, and accepted as real by the other players, ESPECIALLY if you actually have a handkerchief or feather in your inventory.  You might also want to work on a collection of things that you fancy, or that define the character you are stepping into.

Other RP items can be combined into other usable items, or collected, or help you whenever a role related decision is pending. For example if you wish to build yourself a pub, getting related items that could be used in a pub, makes the big difference compared to someone that just sais he has a pub somewhere, and you will receive official support in roles and events you can organize. 

Items are a warmup for this things you wish to achieve in this realm.