Walk. 33% grade is heavy work even when walking. For most of us (your case does sound unusual) having to walk once in a while makes more sense than rigging an ultra low gear that is only rarely used but must be carried along all the time. At 33% it also gets difficult to keep front wheel on ground. If you decide you have to have sub 1:1 gears it is easier than it used to be, can be done, but trouble, expense, not encouraging that path until you are sure.