Some meals carry a surcharge (premium price). Included Surcharge Meals is how many surcharge meals per delivery day the customer may pick without paying extra on this bundle. The column header tooltip says "Per Delivery Day".

The maximum allowed equals the smallest "days' worth of food" number among your delivery days (a bundle delivering 3 days on Monday and 2 on Thursday can include at most 2). Entering more returns "The included surcharge meals value should have a max of N". The value is copied onto each new subscription. If you want Sprwt to auto-pick included surcharge meals when auto-selecting, enable Order: Subscription > Allow AutoChoose Included Surcharge Meals?.