We always did Donuts with Dad (then include Grandfather, Uncle, Male Guardian, etc in the tagline) as not to exclude anyone (same goes for Muffins with Mom just change the gender
Some do just Donuts/ Muffins as a social event (your goal is just to get parents involved)
Some do alongside (ie bring/read a book, cangoods)
IMO the simpler the better - I think they both should just be a social (and maybe here's what the PTA/O's and school do and why parental involvement is important) not a fundraiser/ collection of any sort.
IMO school and PTA/O's should foster community/ parental socialization/ education as well as involvment - this event could fit 1- 2- or 3 ideas
Some RSVP (as to get a food count) and some dont