I found a wonderful candidate for Katy's favourite category: words that would be connected if they were totally different words. But unfortunately I could only find two of them: mine and mayo. How fun if the category was Words that are occupations if you put an R last 
Good one! Now, of course, I'll be trying to think of other candidates.
Many occupations are words that combine the activity with an R, I'm realizing (serve and server, etc.), but the vast majority don't make completely unrelated words (like MINE and MAYO) if you remove the R.