This time of year there are many people who hate shopping. The shops are packed, the lines are long and who knows if what you want is even going to be there? Many people would happily pay someone to do it for them. If you are shopping anyway, this is a great way to earn extra money. Mind you, it can be stressful, so is not really for the faint hearted.
You can advertise in school newsletters, the paper, or flyers at the shops.
It is up to you how you charge. You could charge a percentage of the present total, you could charge hourly or if they have a specific list, research it and find the items for less than RRP and take either the whole savings e.g. 1 item you find is 20% off, another has $10 off, another has $40 off etc… you keep those “savings”.
You will need to be organised, plan you trip and take into account what fits into your car, how you are going to get it home, will people pick it up from your house or will you deliver, how much petrol will be consumed if you are going to a few shops etc…
This could also be done with groceries or birthdays during the year. Since we have to shop, why not make money doing it?