I didn't, it didn't seem worth being held up, but I could have. It happened at the checkout. The cashier had just run all my stuff through and told me the total, then the woman behind me audibly gasped and said to the man with her "So much money! You could feed a family for that!"
The silly thing is that's exactly what I was doing. Most of the food is for when my fiance's parents come to stay with us (no matter what they say I know they eat nearly twice what we do, so to my mind it's more like feeding 6 people than 4).
But even if I was the single student I looked like (jeans, uni hoodie, headphones, backpack) who's to say I didn't live in a house where we take turns shopping and cook/eat together? Or maybe I was doing a favour for a relative or...so many reasons I can think of a seemingly young person would be buying a 'family' shop alone.
(Edit: here I am commenting on someone else's assumption when I realise I called the couple husband and wife when I have no idea what their relationship is!)