I suppose this is a bit late now, but if it was me I'd turn it around, and imagine a tin of tuna that had been sitting on the shelf for 10 years watching the customers of the supermarket. You could then talk about what the tin has seen; the way shoppers' behaviour has changed over the last 10 years. If there's some food standards issue that relates to changes in shoppers behaviour you could use that to bring the presentation back to some 'food standards shop talk'.
Risky, but you'll stand out among 5 other people showing powerpoint slides with graphs of typical salt levels.
---------- Post added at 21:45 ---------- Previous post was at 21:43 ----------
PS 5 minutes is not long at all - make sure you time yourself in the practice run
