While you can certainly eat dehydrated food dry, for most recipes you will want to re-hydrate your veggies and meats before making the meal. Re-hydrating can be done simply by soaking your food in purified water, and the process can be accelerated by heating the food.
Re-hydrate food fastest with boiling water
Re-hydrating food goes fastest in boiling water. Place your dehydrated vegetables and meats in your cooking pot, add enough water to completely cover the food, then bring the water to a boil. Keep adding water as necessary to keep the food covered. The heat will break the cell walls of your foods and allow water to permeate it faster than simple cold soaking would. The food will cook as it soaks up the water, so you can use it in recipes without additional cooking. You can re-hydrate most foods in 10-15 minutes this way, but the time will vary depending on how dry and how large the pieces of food are. The best way to find out if food is completely re-hydrated is to taste a piece.
Save fuel by soaking
Fuel is heavy. To reduce the amount of fuel you need to cook your meals consider pre-soaking your vegetables. Dehydrated vegetables including beans, (but not leafy greens) should be packed in zip-lock bags separately from grains. One to two hours before the meal cover the vegetables with purified water and allow them to soak -- add water as needed to keep the vegetables covered, they will not become over-hydrated using this method. This will reduce cooking time significantly for things like carrots, zucchini and onions. Leafy greens and quick grains like noodles and parboiled (instant) rice do not require soaking and in fact, their texture will suffer if you do soak them.
Hot soaks are safer for perishable ingredients
It is not safe to soak meats at ambient temperature unless it is quite cold, but if you are short on fuel you can place dried meat and clean water in your cooking pot, bring it to a full rolling boil, turn off the flame and cover it with a tight lid. Let it soak for 1/2 hour without taking the lid off then bring it to a full boil again (adding more water if needed) before eating it.
Spilling food on your belongings can attract animals so it is important to avoid spillage while you pre-soak your food. I like to eat as soon as I get to camp so I pre-soak my veggies in my pack while I hike. Zip-lock bags are not usually waterproof and will leak in your pack. To avoid spillage, I put my water filled veggie bag inside my cooking pot, place the lid on the pot and pack it upright in my pack with other gear packed in tightly on all sides. This is not foolproof -- you have to be careful not to tip your pack on its side when putting it on and taking it off, but it works well and it allows me to have my evening meal soon after I arrive at camp.
Prevent Bacterial Growth
Getting food poisoning could certainly ruin a camping trip, and in the back country it can be life threatening. Food-safety rules shouldn't go out the window just because you are on vacation. You must use purified water to soak your food and you should always cook your soaked foods completely before consuming them. I don't recommend soaking vegetables for more than a 2 hours on cool days, and 1 hour on warm days. Soaking meat for more than 1/2 hour at ambient temperature is not safe unless it is below 40F/4C degrees and you can protect your food from sources of heat such as body heat and campfires.