Well it depends a bit on what you like and what you normally eat! No point buying chia seeds and kale if you hate them or steak and chicken if you are vegan!
I'd try and do a meal plan before you go and plan out some tasty balanced meals you know your family will like, include at least 2 portions of fruit and veg in each meal, some lean protein (things like fish or chicken if you eat meat, or beans, pulses or meat replacements like quorn if you don't) and complex carb like wholemeal bread, pasta or starchy carb like potato (unless you are deliberately following a low carb diet). Write down everything you need to make these meals, do a bit of an audit of your fridge, freezer and cupboards and cross off what you already have. For my household this looks like:
-Porridge (+milk), wholemeal bread for toast, butter, juice, greek yoghurt and fruit for breakfasts
-Stuff for sandwiches, salads, crudites and hummus and soup (I make my own, but shop bought is fine) for lunches (or sometimes we eat leftover dinners for lunch), with more fruit for afters
-Family dinners, things like stir frys, curry, chilli, pasta dishes, stews for dinners, with yet more fruit and yoghurt, or cheese, chutney and crackers for afters!