Listen to what customers really need. You are missing a large population of potential customers but not marketing to single people, who need smaller portions and meal receipes for one person.
Why not have something new and fun, like Holiday Boxes. Meals based with food for specific Holidays, i.e. Christmas, Thanksgiving, Easter, Passover, July 4th, AND
International Boxes once a month or Quarter with food from a region/country that would be fun. For example. Aussie Box. England Box, Canadian Box, Southern US Box, Midwest US box.... etc. Come on now be creative.
Also be more flexible on payment plans. Perhaps have a 6th month memership. 1 year membership someting like that.