Every item page shows two choices above Add to cart: One-time purchase and Subscribe & save with a weekly / 2-week / 4-week rhythm. The choice rides along to the cart and checkout, so one click on the item page is all it takes. Members who already subscribe see an Add to my subscription button instead – one click adds the item to every future delivery.
When a subscription begins, the member receives a plain-words welcome email (what repeats, when, how to change it), and each cycle they get a heads-up a couple of days before the ordering deadline with edit / skip / pause links. They can change items, frequency, skip a week, pause, or cancel themselves under My Account → My Subscription – no phone calls needed. The Subscribe & Save discount is your setting; subscribers’ foods are also reserved before anyone else’s each cycle, which is worth mentioning more than the percent.