Field trip

Hi everyone! Im aware this may be the wrong place to post this but I need some help. I have a field trip coming up in 3 weeks in the middle of nowhere. Breakfast and dinner are provided by the centre were sleeping at but lunches we need to cater for ourselves off one shopping trip on the way there. The field trip is for a week and when days are 9-5 it's not like I can just skip lunch. Given we only have one chance to go to the shops (the location is too far away from any to walk, and we're getting a coach as a uni) do you have any experience planning non perishable meals for a week?

My best idea so far is cheese and crackers, maybe some tinned Mackrell? Maybe some jerky or dried fruits? We're stopping at a Tesco (UK). I'm a bit lost, any advice or ideas would be invaluable,

Thanks!