I've done bag packing in our local supermarket in aid of our Scout Group a few times, and the trolley loads are fascinating. We've often got 23rd December, which is manic, and a real mix of "the end of the world is nigh, buy everything" piled high, just the luxury items like flowers/bubbles and a side of salmon (hostess gifts?), just the regular weekly shop types, and a few who only have a handful of big items (a turkey, ham, side of smoked salmon and 2 family-sized lasagnas with a spare bottle of milk and cream thrown in).
Also, while I never have to do the shopping for our Cubs (we have a great parent who looks after that), I have noticed a few times trollies that definitely look like shopping for a residential trip - loads of bread, stacks of packs of sliced ham and ready-sliced cheese, at least 2 jars of nutella, 2 boxes of cereal, 5/6 bags of fruit and 4/5 multipacks of crisps, 10 cartons of juice and 20 litres of milk, only 1 jar of coffee but a large box of teabags and 4 jars of hot chocolate powder.....
An adults' residential trip tends to have less cheap stuff (and fruit), and more sharing bags of crisps, mixers, alcohol and things to nibble (nuts, pesto and hummus, breadsticks etc), and the makings of either a fry up or fruit and pastries breakfast (and a LOT more coffee!!).