I work at home, so packing my lunch isn't an issue, but many of my lunches consist of what I call deconstructed butties. In that whatever I might have stuck between bread slices, I just eat with my fingers or a fork, without the bread - and probably a bit more of it too. Cottage cheese, coleslaw, pate, cheese, sliced meats, tuna fish, olives, tomatoes, salad etc. My husband (non-diabetic) likes doing this too and we have a lot of airtight pots he just puts things in and puts in his insulated butty box for work.
Depending on how many carbs you want to ditch, you sometimes just need that crunch, so I add either a few crackers that have lower carbs (most supermarkets have some biscuits for cheese that are under 3g carbs each - often cheesy or seeded ones), cheesy oatcakes (a bit more substantial than crackers) or a broken up popadom - they replace crisps for me - each one is 3g carbs. Just stick some nice butter on your biscuits and it'll feel like a proper lunch with many less carbs. You could eat 4 buttered cheesy oatcakes for the carbs of one slice of normal bread.