Hey Mandy that should be perfectly manageable. I have not yet poisoned myself despite being in an office without access to a fridge. Most things keep really well as long as they are properly cooked. They might not taste quite as nice if not really cold (yoghurt is like that for me), but they will be safe. As suggested, you can get really small cool packs that won't weigh you down (about the size of those individual ketchup sachets you get in cafes) - I have seen them sold in John Lewis.
This morning I put a couple of them frozen into my (insulated) lunch bag at about 7am, they are defrosted now at 12 but everything in there is still pretty cool and will be so for a few hours yet - it of course helps if you keep everything in the fridge before packing your lunch.
If you're concerned about the extra weight - freeze a small water bottle and use that instead, and you can then drink it when defrosted at lunch time.
As for what to take, let your imagination run! Anything can be baked into a crustless quiche: chicken, ham, veg for PV days. You could even make an oatbran base using the normal galette recipe and pre-baking for 20 mins.
Cold meats with mustard sauce (I am having a few slices of beef today).
Any fish, hot smoked, or tinned. I pile a bed of lettuce leaves and tomatoes into a 'tupperware' box, season a little, sprinkle with vinegar and the put the fish on top. Put a lid on and it's ready to go - remember to pack a fork!
For quicker eating options think fingerfood: beefburgers, chicken legs, boiled eggs, surimi sticks (in limited amounts)
Invest in some of those 'lock&lock' type poxes - they really are watertight and I carry 'saucy' things (yoghurt, sauces made with fromage frais, soups etc) in them with no problems.
Good luck! We'll be waiting to hear how you get on.
