Hi Katy. I have been dehydrating and vacuum sealing my meals for 6-7 years now, and this is easier than you think. I usually will keep my dehydrated meats in the freezer, or at least in the back of the refrigerator. Those are the most susceptible to spoilage, due to the fat content. If you are a meat-eater, I would suggest for you to do the dehydrating of sausage, etc. just a few months before your trip, and keep it in the freezer/fridge after vacuum sealing it. If a friend is sending you re-supply boxes, have him/her do the same. I expect that an unrefrigerated pack of meat would not spoil for maybe 2-3 weeks if kept out of the sun.
Most of my meals are made from freeze-dried ingredients, which are very stable for 4-5 years when vacuum sealed (I buy Mountain House's #10 tins and re-portion things into individual meals). My store-bought dehydrated ingredients, like veggies and fruits from Harmony House, seem fine over 3-4 years. The non-meat items I dehydrate myself, when vacuum sealed, remain good for at least a year, usually 2-3.
Using freeze dried or dehydrated ingredients allows one to create custom meals that pleases the palate. You can add your preferred spices, specific ingredients, and control the ratio of fat/carbs/protein and desired amount of calories–all at a rather low weight.
Here are some examples of my favorite meals, with calories, packaged weight, and calories per ounce carried:
1) A 15 oz. can of Stagg Silverado chili, dehydrated: 520 cal, 3.4 oz., 153 cal/oz.
2) 10 oz. of Bush's beans + 7 links of Hillshire Farm's Little Smokies sausage (all
dehydrated): 551 cal., 3.8 oz., 145 cal/oz.
3) Dehydrated Tasty Bites Jaipur veggies, FD chicken: 453 cal.,2.8 oz., 162 cal/oz.
4) FD mac/cheese + peas, dehydrated Spam: 542 cal., 3.7 oz., 159 cal./oz.
5) Mac/cheese, burger, peas (all FD): 495 cal., 3.5 oz., 141 cal./oz.
Freeze dried ingredients reconstitute quickly, of course. Most dehydrated items are slower, and need to be presoaked or simmered for a short while. To speed up the process, I cut the sausages and Spam into thin slices before dehydrating. My method of cooking can sometimes be a bit fuel intensive if I need to do a lot of simmering, which depends upon what the meal is. The Stagg chili, for example, requires that I fire up the stove for 30 seconds several times over 1/2 hour, and stir it, to properly rehydrate the goodies.
If you will only be doing freezer bag cooking, you will need to carefully choose your ingredients. Some things just don't rehydrate quickly. And don't forget the olive oil to boost the calories!