Sainsburys and Tescos both stock the Dietary specials bread and also both do their own brand. All are ok toasted but not much cop for sandwiches. Both also do own brand part-baked baguettes which are better for sandwiches. Sainsburys also do their own bread mix and stock Doves gluten free flour.
Tru-free biscuit range is good - custard creams, chocolate digestives and bourbons. All stocked in Tescos, Morrisons and Sainsburys. I haven't seen a digestive/rich tea type biscuit in any of the supermarkets, but DD1 doesn't really like them so I haven't looked out for them.
tescos do great cheese crackers, Sainsburys and Tescos stock Tru-free herby crackers which are yummy.
DD1 is allowed rice krispies by her dietician, but I know not everyone is (but only kellogs). Otherwise the Kallo honey-coated rice puffs are good or the cornflakes mentioned by others.
Sainsburys, Tescos and Morrisons all do own-brand cereal bars in various flavours, blueberry, apricot etc. Not a fan myself, but they don't look much different to the non-gluten free ones and DD1 loves them.
Sainsburys TTD sausages are not gluten free, but they do their own brand ones free from ones in the freezer section. Otherwise, Sainsburys stock Helen Brownings quick cook organic sausages which are gluten-free and both they and Morrisons stock The Black Farmer sausages which are fantastic.
DON'T try the Tescos pizza bases - like cardboard, but the Sainsburys ones are good if you like thin crust! If not, in their free from freezer section, they'll have the dietary specials pizzas, which are v. nice.
I find Sainsburys labelling is great (haven't got a local Aldi) but it does depend on the size of your local branch - both my local ones have good ranges but a small one near my mum's didn't have anything free-from.
Walkers crisps are good for labelling - all say 'suitable for coeliacs' if they are...salt and vinegar flavour aren't!
Oh and just in case...smarties have gluten in them, but you can eat as many cadbury's buttons as you like .
Hope this helps. Have a good holiday