Go crazy with the condiments (and other stuff).
I always make sure to put out a big jar of that standard-bearer, Hellman's, but it's easy to make your own mayonnaise. For variety, doctor store-bought and homemade with different flavorings. Over the years, we've had scallion, roasted garlic, olive-anchovy, basil, bacon-chive (using rendered bacon fat instead of oil), chipotle, and—my favorite—pimenton (Spanish paprika). One quart of mayonnaise will feed about 15 people.