I'm one of the few people that removed all the plastic cup holders from my tractor when I got her. Use those places for glove storage or whatever. I've been running tractors since the 60's and never felt to need to have a sippy cup of anything with me. If I am really working, I have a gallon or three of ice water with me...though...
Like I said though, I dont necessarily use mine for "cups"; just more of a catch all.