I used to sell quite a lot to restaurants. They will need unit pricing to compare to other suppliers. You might sell tomatoes individually at the market but for the restaurant you will usually need to sell by the pound (weight) or bushel(volume). Many restaurants are familiar with buying in "Flats". That can be 8 quarts or it can be 1/2 or 3/4 bushel. Ask them for their preference.

Be prepared for them to always want a product at a time when you can get more elsewhere. Many restaurants buy for weekend business needs. Once produce auction prices drop they will leave you hanging. I established a minimum order delivery and that was unagreeable to many of them. If you don't mind driving xx miles to deliver a few pounds of something you might do OK. Also keep receipt records because you won't be paid for weeks after delivery.