Are you only doing strict heirlooms that are quite old, or are you doing open-pollinated, stabilized varieties that are potentially a lot newer, too?

Some varieties I would recommend (because I like them) include Edna Slaton's Candelabra okra, some kind of prolific Armenian cucumber (I like Metki Dark Green Serpent), an edible gourd, Dark Star zucchini, Shark Fin Melon squash, Sasha's Altai tomato, Neapolitan pepper, Marmande tomato, Tatura tomato, Sweet Orange Cherry tomato, Ha'Ogen melon, Ananas D'Amerique A chair Verte melon, Santo Domingo Winter watermelon, Verona watermelon, Blacktail Mountain watermelon, Bowling Red okra, Aji Dulce 1 pepper, Ring of Fire pepper, Pink Berkeley Tie Dye tomato, ground cherries (and other seed-grown berries), Crimson Forest bunching onion, garlic chives, Long Island Cheese pumpkin (or similar), some sweet sorghum (I grew Mennonite sorghum this year), George Detsikas Italian Red tomato, Amana Orange tomato, sunflowers with large heads and edible seeds (e.g. Mammoth Gray Striped, Dwarf Sunspot, Mongolian Giant, Titan, etc.), Spicy Globe Bush basil, Aswad eggplant, Sub Arctic Plenty tomato, Cisineros tomatillo, etc.

Some varieties I would recommend (because they're popular and might sell well) include Cherokee Purple tomato, Brandywine tomato (and Brandywine variants), Green Zebra tomato, Pink Berkeley Tie Dye tomato, some kind of honeydew melon, a habanero (orange), Carolina Reaper pepper (world's hottest pepper), a Ghost pepper variety (Bhut Jolokia), a yellow sweetcorn, snow peas, container-worthy varieties, dwarf varieties (dwarf tomatoes from the dwarf tomato project are pretty popular), Stupice tomato, Italian Large Leaf basil, Aunt Ruby's German Green tomato, Charentais melon, Aunt Molly's ground cherry, Pineapple ground cherry, etc.

Anyway, I'm not suggesting you add all of these, but you might look into them.