I sometimes take cold hamburgers or roast beef.

Hard-boiled eggs. I like mashed yolks with butter and a pinch of salt.

Canned tuna, salmon, sardines, or chicken.

Nuts, if they are on your food plan.

I often take a bottle or two of water or tea.

If a larger cool-pack is easy to do, then a container of yoghurt, or gelatin cream. I often tuck in something frozen, which will keep my cool things well, for up to 24 hours.

In cold weather, a thermos of tea, or broth, or even hearty soup.