A selection of sandwich cases and saddle canteens. These leather cases hold either a flask and sandwich tin, or a sandwich tin alone.
They attach to the D rings behind the rider on the side of the saddle.
Traditionally women in the hunting field would not carry a separate saddle flask and sandwich case, but a canteen which would hold both. I don't believe this tradition is universal - I have a 1920's Swaine Adeney catalogue that features ladies' flasks. However, it is upheld by some hunts, and some sidesaddle classes.
All the D rings on a huntsman's saddle are often occupied with horn cases, wirecutters etc - leaving nowhere for a flask or sandwich case - disaster! A solution to this problem is to carry refreshments about one's body, in a case with a diagonal shoulder strap and loops for a belt around one's waist. (Personally I would probably suspend myself on the first tree I met if I tried this, but hunt servants are much more competent than I am).