I try to meal plan, but with a teen daughter its virtually impossible. I have in my head what I'd like to make that week, I know whats in the cupboards/fridge/freezer and I head for the reduced sections first if I can. Worst thing is taking my daughter shopping with me, although I appreciate the extra pair of hands to carry the stuff back, she regularly adds stuff to the basket! I also only ever shop with a basket, rarely a trolley and even when I do do a trolley shop its always a small one
Once a half-term or so I plan on doing an online shop to get bulky and heavy items delivered from Asda. My daughter takes bottled water to school (she does refill them but they get battered, we have tried re-usable bottles but they tend to leak), I buy the biggest but cheapest pack of toilet roll, biggest box of soap powder etc and just add on the weekly shop
I always use mysupermarket to get the stuff as cheap as possible. I have asda and aldi opposite each other at the bottom of my road, homebargains/iceland/poundstretcher a 15 min walk away one way, co-op a 15 min walk another way, 2 different big tescos with butchers & veg shops in other directions so I shop around and walk to them all. Although I do admit I will occasionally pay out for the bus back lol