Dry Sack is a popular brand of sweet, blended sherry, produced since 1906. 

Blended sherry is a composition of different types, in this case Amontillado, Oloroso and Pedro Ximénez wines. Dry Sack is slightly different in the sense that the mixture is returned to a solera after blending. The grapes for Dry Sack are taken from Williams & Humbert vineyards in the Jerez Superior area (Pago Balbaína and Pago Carrascal).

The label Medium means it is sweetened, in this case to around 30 g/l. It used to be called Medium Dry but don’t focus on the confusing “dry” part – it’s fairly sweet indeed. You can drink it on its own, as an aperitif (although I prefer dry wines to increase my appetite) or as a gentle digestif. Another suggestion is to turn it into a spritzer (with Canada Dry for example) or a cocktail (try vermouth)