have you been tested for coeliac disease? It's often misdiagnosed as IBS (it was in me for......oooooooh nearly 20 years anyway)
Sainsbury's do a free from english muffin which is both wheat and gluten free and is the best bread substitute I have found that's available at a supermarket level, but are only OK toasted. I toast them and then make sarnies from those. There are some really nice GF breads out there; juvela and glutafin both do a nice one, but you have to either get them on prescription or buy online.
cereal wise, oats are OK (if just wheat free), but a lot of oats contain traces of wheat due to harvesting/milling using same equipment as wheat. Depends on your level of sensitivity. also, rice crispies, and Nature's Path do couple of wheat free and gluten free cereal that you get in Sainsbury's.
most sausages contain rusk which is wheat derived; same with most shop bought burgers.
Deddie and Andrew's Harrogate sausages are wheat free, as are Black Farmer (available in sainsbury's and the co-op) and a couple in the sainsbury's taste the difference range. Supermarket "free from" sausages taste rank...avoid at all costs. Siansbury's So Organic burgers are wheat free.
Can you see a picture emerging? sainsbury's are one of the best supermarkets ime, I'm not on their payroll, honestly
coeliac uk's food and drink directory is worth the money as it contains lists of gluten free (ergo wheat free) products available from all the supermarkets and is my bible these days.
sorry, bit long winded there!