Each ordering module that supports bags (meal prep subscriptions, à la carte, packs, catering, by the pound, custom meals, and any module sub-options) appears as a toggle in Modules allowed. A bag type is only offered to customers ordering through the modules you tick. When Only For Proposals is on, the list narrows to the modules that support proposal bags. Combine this with Pickup points and Delivery routes to offer, for example, a cooler bag only on delivery routes and a paper bag only at pickup points.