It is such an interesting question, London_Mummy. I found myself thinking about what is a hack, and what do I take for granted? While I make my own stock from time to time, I keep Massal stock powders (vegetarian) on hand. I also use frozen puff and shortcrust pastries because life is too short to be making pastry and we have an excellent brand here (Careme). Other things include tinned coconut milk, the occasional tin of beans or lentils for emergencies, jars of artichoke hearts, frozen peas and beans. When I am having a busy week I'll buy a pack or two of pre-prepared veggies for stir-fries or roasting. I love keeping a bottle of Australian-style tomato sauce in the fridge, and you might find some hoisin sauce and/or black bean sauce there too. Chilli crisp is a must.
But I think the biggest hack I have is to use store-bought bottles of passata in place of some of the tomatoes in recipes where they will be cooked down, such as Indian dishes. It is more reliable in flavour than fresh tomatoes and cheaper than either fresh or tinned tomatoes. If the recipe calls for 3 tomatoes, for example, I'll add one and some passata. Or if I don't have tomatoes, I'll just use passata.
Mostly I like to cook from scratch, and make many of my own powders, pastes, pickles and ferments. I freeze a lot of produce from our garden (including tomatoes so some of the year I don't need to use passata), and also dehydrate home-grown fruits, veggies and herbs. I precook many beans and lentils and store them in the freezer. I do these mainly in spare moments and they are usually not labour intensive.