This is a good topic and of course depends on your refer size and config.
Our refer has a hold over plate in the after section which is obviously the coldest part. It can be brought down to freezer
temps if we keep running the compressor
We keep the most perishable items near the plate and then comes the most frequently used.. Milk Juice. Cans on the bottom. We use smallest size like quarts instead of half gallons because as the become empty they take up too much space for the volume of the container.
Use tupperware to segregate things together like butter, cheese and so forth.. cold cults.
A good approach is to bring some frozen meats which will keep the box cool and you can prepare and eat them as they thaw. Same applies to pre cooked and frozen meals
Another approach is too keep all the drinks in a separate cooler with ice and leave the refer for only food
Think of meals
which don't require a refer... like pasta and so forth.