We have two menu options for dinner: chicken and pork. However our venue will accommodate any vegetarians/vegans/gluten free, etc without us having to "offer" those options on the menu (and pay an extra $5pp for the 3rd menu option) as long as these special meals account for less than 10% of the guest list-which would mean a maximum of 10 people requesting something special.
I can't decide whether to put a line/note on the RSVP card for people to mark any allergies/special dietary needs (And risk getting a bunch of things like "no onions" "I don't like garlic), or listing "chicken", "pork", "vegetarian" (and risk more than 10% of the guest list choosing the veggie option just because they don't like the sound of chicken or pork), OR just not listing anything at all and assuming anyone with a special diet will contact us.
There are three people I definitely know are vegetarians, I have no problem just calling or emailing them and letting them know about the "silent" veggie option. But there is a chance that there are others I don't know about.