Have a cup but will only use if doing a tremendous amount of groundwork as I find it digs in too much. It is a hockey cup so maybe if they design one specifically for grappling I would certainly take a look at it. When doing armbars if you don't get in close enough (and you should), then your opponents elbow is right on your groin and without the cup it can really be bad news. Also all of that rolling around it wasn't until recently that I got kneed twice that I even considered wearing one.
I also have the mouth guard but will only use when we do full contact from stand up, to take down, to grappling and ground 'n pound. Otherwise unless you compete it may not be needed.
Knees have never bothered me so have never considered pads. Did some long day classes where many had sore knees and said they were going to wear them next time but "so far" I have not felt I needed them.
"IF I COME ... I'M BRINGING THE PAIN WITH ME"