There are a lot of sites devoted to covering the "Secret Menu" though they mostly all list the same things.
You can even find one abbreviated listing on In N Out's own web site.
When not doing low carb, it is a Double Double Animal Style, no pickles, fries and an extra large iced-tea. On low carb it is a 3X3, Protein Style, Animal Style No Pickles and an iced tea (no fries - duh). I like to enjoy a cheddar Thin Krisp with this if I can.
Susan gets a Cheeseburger with grilled onions and spread only, fries and a medium or large Coke with extra ice.