To spend almost nothing, there are several assumptions (besides the obvious, no spa, no excursions):
no alcohol with meals - if you bring your own wine there is a good chance you will be charged a corking fee of $15 (of course, not drinking is certainly an option)
no palos - ooo to miss this, well OK
bringing your own floats and snorkle gear to CC, might not be that easy and still costs something
the picture at CC with Mickey and the ship in the background (which now sits on my desk at work) was, I think, $10 and worth every penny
you must press your own clothes - the $12 I spent (for pressing service only) was worth the hour (at least) I would have spent in the laundry room
Just my opinion - I am frugal - cheese platter in ziploc at the shows, room service cookies and bagged chips from plutos at the movies, etc...but there are some things that cost money on the cruise that cannot be avoided unless you go without.
Barbara