I'm thinking that there should be points given to a player after they complete a task, and there should be a shop created so that you can spend the points in that shop.
Like a pvp store, but you get the points from doing slayer.
I don't recommend putting items such as phats, or any other rares in this store, or everyone will constantly do slayer and everyone will have partyhats etc..
^Just a suggestion.
-Courtney.