Flasks, cup sets and vacuum flasks for the peg, the high seat and the back of the truck.
Hip flasks
Pewter is the traditional choice and the one that gets handed down — Bisley's 6oz kidney and Gamekeeper flasks are the classic shapes. Leather-covered flasks from David Nickerson run in 6oz and 8oz, some of them as a flask-and-cup set, and one as a full leather travel bar.
Cup sets
Bisley's leather-cased sets come in 2oz and 3.5oz, four cups to a case. Four is not an accident: it covers a peg, or a rifle and a stalker, or a truck full of beaters, without anybody having to drink out of the flask itself.
Vacuum flasks and mugs
Jack Pyke's cartridge-pattern vacuum flask and the Deerhunter mug are the everyday end of this. Soup at midday does more for a January driven day than any amount of pewter.
See also game shooting accessories and larder.