Time outside
Plan a picnic you can carry on public transport
On public transport, everything in the picnic gets carried both ways. Give the assistant your bags, the time you will be out, the journey length and any dietary needs, and ask for a packing plan.
What to check in the answer
Time and temperature limits for perishable food come from official food safety guidance, so confirm them with your national food safety agency instead of relying on the assistant. A plan that works on a cool day may not work on a hot afternoon. Check the park's rules too, since some parks restrict glass or alcohol.
Your next step
Estimate the total weight of the bags on the way out and ask whether you and the seven-year-old can carry it comfortably. Then ask for a revised plan for the trip home, when the food will be eaten but the rubbish, empty containers and any leftovers still need carrying, and say how much room you will have in the cool bag and tote.