The likes of home made soup, stovies etc are super cheap to make and could be sold on cheaply while still making a decent profit but it would require a committed volunteer to take on the catering on behalf of the club.
Without that, you have outsider caterer charging what they want and I assume the club getting a percentage of sales or a set fee for the pitch. No hassle for the club, potentially less income but also no waste to deal with for example.