We always grow potatoes, wild garlic (bear leek), onions (tops), spinach/ mangold, thyme, lavender, rosemary, blackberries, apples and cob nuts.
We rotate in pumpkins, long beans, lettuce, corn and kale, depending on what the kids want and how much space we have left. We have a few allocated areas in the garden and I am always sneakily trying to forge out more space DH isn't green inclined, but likes to eat stuff from the garden.
My biggest investments have been tools to be honest. They often break or disappear because of the kids we no longer have a compost patch because of the inquisitive kids, but have lovely friends who bring and give us their extras from time to time. We have started to incorporate localised composting (essentially dig in a few localised spots in the summer months, insert kitchen non meat food waste, add urine (boys will help with this quite happily), and then cover and compact down).
Food gardening can save you money. You need to hold on to the seeds and be willing to exchange/share. My local Friends of the Earth association has a yearly Plant Market, where seeds, plants and tools are exchanged or donated. They give great tips (localised composting for example, or what grows well in the region based on the light levels).
Our favourite meals from our garden are shepherd's pie (the potatoes and veg), stir fry or soups. Equally you can make your own lavender bags for your cupboards or drawers.