Both food and water affect your energy repletion rate. Keep some green in hunger and thirst and you will be able to perform actions for a longer period of time than if they are empty.

Food: Different types of food will fill you up in varying amounts. Some will fill you up most of the way with one item, other may take multiple items. With fish, the cutthroat and mountain whitefish are the best. With plants, the huckleberry oak does a good job.

Water: any water source will do. I suggest filling up on water first before eating if both are low or empty. Water is free. Food you have to obtain.

Stop and take in the sights now and then. Chat with a neighbor. Do some crafting. Don't wait for your energy to be fully depleted to let it regenerate.

If you want to travel long distances quickly, travel as light as possible. Encumbrance will slow you down. Use the roads if they are in the area. If you are gathering/scavenging/foraging in an area, carry a second container and set it down. Return to it now and then to transfer your found items. Once done, drop your current pack, pick up the bin, then transfer your items from the pack to the bin and pickup the pack.

There are rumors of a rest command, but I haven't seen anything lately. There is a rest command keybind, but it is not active as far as I know.

Managing your energy will be important in game. If you are playing now, it is a good time to set up some habits to keep from getting too low and getting into trouble when exhausted.