The oldest flour I could find packed in Mylar bags with a oxygen absorber were from March 6, 2011 so they are only 10 months old. I opened one up yesterday and there was no odor what so ever and I baked 2 beautiful loaves of bread. I will keep experimenting opening one of these bags each month or so to see how long it last before it goes rancid. Using the food saver bags were a bust. At least for flour stored 3 years in them. Now I am wondering about other food I have in them.
I love the Mylar type bags I get from the LDS. They are 7 mils thick. If you are really into saving, they can be washed, dried and reused. I wash mine in the dishwasher and then place them over a mason jar on the counter to dry. They are that strong. I cut them in half for smaller size items I need to store.
I use a iron on a high setting to seal them. You don't need a fancy machine.
One of my goals this year is to dehydrate a lot of items. I'll be putting a few things in jars but a majority will go into the Mylar bags. Dehydrating takes up way less room and are as light as a feather.