At the beginning of every new decade, I'm reminded of that old adage: never food shop on an empty stomach. Or, always food shop on a full stomach.
That way you'll buy only what you need.
By the way, you can have a full or empty stomach when you swim. The whole cramps thing is nonsense. But, if you're buying a swimming pool, make sure you drink some chlorinated water first.
I use this philosophy at the liquor store. Yesterday I went to the LCBO hammered and came out with only 6 litres of vodka. Way less than I normally buy. Saved a ton.