Smart shopping: any good tips?

As part of the financial capability scheme I'm volunteering for, I've been asked to prepare a 40 minute presentation on 'smart shopping'.  I need to get this done before going on holiday in ten days' time, and am quite busy with various other projects in the meantime.  While I gather my thoughts, I thought I'd - rather cheekily - invite suggestions....  I would love to hear from you if you have any suggestions for tips you think I should include.  The audience will be a group of older people living in sheltered housing; the main things they need to pay for from their pensions are food, clothing, entertainment, and Christmas and birthday presents.