Start by doing a stock-take of the things you already have in your fridge, freezer and pantry - you've probably got more than you think.
Make a meal plan for the week that includes breakfasts, lunches, dinners, snacks etc. Make sure you take leftovers into account. For example, if you are making a roast for dinner one night, you can plan to use any leftovers in wraps or tacos the next night. Get the whole family involved in the planning, each person choosing what to cook each night.
Create a shopping list based on your plan and you should only need one trip to the supermarket (market research shows you spend more overall at the supermarket when you make multiple visits in a week compared to just heading in once a week).
There is an app for that
Take your planning online and make your shopping list on your phone.
There are also plenty of mobile apps for making a food plan and generating the shopping list.
If you're feeling especially organised, there are even apps for tracking the contents of your fridge and pantry.
Check out your mobile device's app store.
(tips: read the reviews, and select an app that is regularly updated)