At some point many outdoorsy types will consider getting two items: A food dehydrator and a vacuum sealer.
Both are worth the investment. Drying your own food is easy and can be a big savings on many items, especially if the only other way to find the item is online and being shipped in the mail. Some items are cheaper or less of a pain to just buy, such as chopped onions but overall after a couple years of hiking meals your investment is paid back, both money wise and in eating better tasting meals!
What to look for in a dehydrator:
I currently have two dehydrators. One is a Nesco. They are affordable, and found at most big box stores and online. While not overly fancy they do the job and work very hard.

Nesco American Harvest FD-61WHC Snackmaster Express Food Dehydrator All-In-One Kit with Jerky Gun
Nesco American Harvest FD-61 Snackmaster Encore Dehydrator and Jerky Maker
Extra "fruit leather" tray liners are available for Nesco machines:

Nesco American Harvest Fruit Roll Sheets for FD-27 & FD-50
Parchment paper for lining trays:
My other and prefered dehydrator:
This dehydrator is a work of art, visually pleasing and whisper quiet. It comes with trays that are designed for small items as well as fruit leather trays.
Making your own dehydrator:
An easy to make and affordable dehydrator can be made on your own with a few furnace filters for racks, bungie corded to a simple box fan. This works real well! In some cases it is better as it does not use heat, so it will not cook your food as it dries. See here for the Alton Brown 'Good Eats' method.
For more references on drying food at home, these books can help:
Food vacuums:
Food vacuums are a great way to preserve your dried food. Especially if you are doing the food in the winter for the next year. I use Food Vac. You can find them at most big box stores and online. The best buys are at Costco and Sams Club where you can get kits, heavily discounted.
With a little work and time, you can have a year's worth of trail foods!

Comments
Dehydrating
Thanks for adding a section on dehydrating. A few recommendations: consider getting an Excalibur dehydrator. It has 9 big trays, and it's built to last. Mine is over 20 years old and has been used heavily. Also, consider getting a mandolin slicer for making uniform slices that dry evenly. One of our favorites is dried orange slices - they take about 24 hours to dry, but they're one of the best tasting snacks for the trail.
Another favorite recipe is making "Endurance crackers" with a combination of chia, sesame, sunflower, and pumpkin seeds. Various things can be added to taste (onion, garlic, dried fruit). Once dried, they're a good trail snack that provides plenty of calories.
cosy?
What do you mean by using a "cosy" to rehydrate food? Is that something that I need to buy? Can you just use a pot, pour in boiling water and let it sit covered for a several minutes?
On Cozies
This is a cozy. A cozy is anything that insulates and keeps heat in, allowing food to rehydrate quicker. Can you use a pot? Sure. There are also pot cozies made as well.
How long will dehydrated beef last?
This is perhaps the most important piece of info and it seems to have been left out.
It is covered on this page
http://www.trailcooking.com/dehydrating101/hamburger-and-canned-meat
With dehydrating meat you will want to use as low fat meat as you can. Once dry, store in your freezer till time to use. Cycle through your dried meat within 6 months.