Some ideas...apologies if I am recycling any of your staples...
For the future shops, if you could add some tinned tomatoes to that when you shop you'd extend your range a bit- bolognese, chillis etc, plus they are cheap and take well to slow cooker meals, though there are an ibs trigger for some.
Vac packed beetroot is a good cheap standby too- add to diced onions and carrots as the base vegetables in a tomato sauce. Really good source of iron. Similarly frozen peas, sweetcorn, mixed veg and spinach- cheap and good source of vitamins. Easy to chuck some in a fried rice, pasta sauce, in tothe slow cooker for the last hour or half hour of a stew.
Bacon, onion and potato frittata topped with some cheddar. Or basically the same ingredients for a dish called russian potatoes- basically a potato gratin made with a bit of cheese sauce, with or without cream, with bacon and onions (fried til soft) in between the potato layers, topped with cheese and baked. Keeps out the cold for definite.
Make pasta dish with sausages, cream and diced celeriac and a bit of chilli/paprika and some parsley/oregano basil or similar spices/herbs.
Or pasta carbonara- boil pasta, grill bacon, grate cheese. Stir pasta into cheese til it's melted then stir in bacon and some beaten eggs with a dash of cream plus salt pepper and parsley or similar dried green herb. Stir till eggs thicken into a creamy sauce. (you can laso do this with sausages in place of bacon, or with chopped pork from roast the day before)
Boil some of the carrots and swede and mash together, serve with roast pork and frozen mash. Second day dice the pork and make a stir fried rice with pork, eggs, onions (add eggs to pan first, scramble then add rice etc)- add chilli, garlic powder, chinese five spice etc to taste. if you prefer you could use the pork and rice to make a slow cooker jambalaya, sausages would also work for that (no need for seafood as many jambalayas have, but tin of tomatoes would help for this, as would some frozen peas) allrecipes.co.uk/recipe/9410/jambalaya-in-a-slow-cooker.aspx- any type of meat can subsitute for the sausage in this really- roast pork, chicken thighs etc
Cheeseburgers with potato buns- cut thick slices of potato, brush with oil and cook in oven at 200C until browned, make burgers from mince and top with cheddar. Use potato slices as you would buns. Add bacon/onions if you like.
Use slow cooker to make a stew- fry diced onions and carrots til soft, brown stewing steak, add to stock and diced potatoes in slow cooker and switch on slow cooker. Herbs and spices to taste, or make a beef madras if you add curry powder to the carrots/onions. Serve with rice. If you get frozen spinach in future weeks, a bit of spinach added to the curry at teh end of cooking will make it a beef saag.
Second lot of mince- you could make dirty rice, sort of a fried rice but with mince through it. doesn't look a million dollars but tastes ok. Think there woudl be a way to do this in a slow cooker. Also sheperds pie with potatos or frozen mash. Or meatballs simmered in stock with a potato gratin.
Celeriac is good mashed together with potatoes or used in a potato gratin too
BTW, I have ibs too and have found avoiding wheat (pasta), dairy and onions help too, although I do realise not everyone has the same triggers, so apologies if these are safe for you.