I know a lot of you are already well-versed in bulk food storage, but I don't remember seeing a write-up with photos in the past, so as I was prepping some stuff tonight I grabbed the camera and took some pics. I'll try to throw in some helpful links along the way. I have to give credit to the guys at P.A.W. Productions for producing some excellent instructional videos on this process.
I'm going to be putting up a 50-lb. sack of wheat flour:
Things you'll need for this:
Mylar bags:
I got mine from USA Emergency Supply. These are the 20" x 30" Mylar metal liner bags. Cost was $1.92 each.
Oxygen absorbers:
I also got these at USA Emergency Supply - a bag of a hundred 500cc absorbers was $11.97.
Buckets:
These are 6-gallon buckets - any bakery, deli, sandwich shop, etc., goes through dozens of these a week, so there's no need to pay for 'em - just be friendly the next time you go in to buy something and ask them. Much thanks to Paladin1 for hooking me up with these.
Mason jar w/ band & lid:
You'll need this to put your oxygen absorbers in after you open them. I stole these out of my finacee's canning supplies.
An iron:
This is what you'll use to seal the Mylar bags once they're full. **CAUTION**: DO NOT, UNDER ANY CIRCUMSTANCES, USE YOUR WIFE'S / GIRLFRIEND'S / MOM'S GOOD IRON FOR THIS!!! If they catch you doing this, you are in for a world of hurt. The iron is one of those things women are extremely protective of, much like the "good scissors". If you do it without their knowledge, and then they use the iron and ruin one of their good tops because you got gunk on the iron, you might as well join the French Foreign Legion. Go to Goodwill and buy an iron for a couple of bucks (hell, you can even get a brand-new iron at Big Lots or X-Mart for under ten bucks). Other options I've heard of are curling irons (see previous warning) or hot jaw sealers, which I'm too cheap to buy, but might be worth it if you're going to be doing LOTS of bags.
Things you don't necessarily need, but might make your life easier:
Bay leaves:
Housewives have been putting bay leaves in their dry goods for years as a method of keeping bugs away. Lots of people think it's bunk, but we've been doing it with all our stuff for years and have yet to find any bugs, so, whatever. Use 'em or don't, it's up to you. They're cheap enough that I'll keep using them.
Gamma seal lids:
These are nifty lids that feature a collar that snaps onto most 5- or 6-gallon buckets, and an airtight lid that screws into the collar. These are especially nice for when you get into your preps, you can leave the stuff in the container and re-seal the lid. I got mine at Homegrown Harvest for $7.99 each, but I just saw that Sportsman's Guide has them for a buck less.
So, stick your bags in your buckets:
I folded the tops of the bags down around the mouths of the buckets at first - this is just to keep it from flopping around and getting in my way at first. Once the bags have some weight in them we'll pull them up.
Throw in a few oxygen absorbers and a bay leaf:
If you do the math, you technically only need two oxygen absorbers for a six-gallon bucket - I'm using a few more than that because 1) they won't hurt anything, and 2) a bag of 100 absorbers is probably more than I'm gonna need for the rest of my life.
IMMEDIATELY put your oxygen absorbers in the mason jar and seal it:
As soon as you open that bag, the absorbers activate. Putting them in the jar ensures you'll be able to use them later.
Start filling your bucket. Obviously, this is easier if you have two people an can just pour it in. I was working alone, so I used a medium-sized mixing bowl as a scoop.
When you get to the halfway point, throw in a few more oxygen absorbers and another bay leaf:
At this point you can pull the top of the bag off of the rim of the bucket:
Pull up on the bag and shake the bucket around to get the flour to settle.
Keep filling your bucket. When you get near the top, throw in a few more oxygen absorbers and another bay leaf:
Once your bucket is full, you're ready to seal the bag. The method I used was to hold an old book behind the bag, and take the iron and go over the edge of the bag until I started to get a good seal:
(Don't set the iron too hot - 3 or 4 should do the trick). After I had the bag pretty well sealed, I tipped it over so I could lay the edge of the bag flat on the book and REALLY make sure it was sealed:
An easier method of doing this is to set the bucket on the ground, and lay a piece of 2x4 across the mouth of the bucket to give you a surface to work on. I didn't have any spare 2x4's, so oh well...
Fold the sealed end of the bag into the bucket:
Put the Gamma Seal collar on your bucket:
You'll probably have to press HARD in one spot to get the collar to seat on the bucket, then take a mallet and tap around the edge to secure it to the bucket all the way around.
Put the Gamma Seal lid on...
...and label it with permanent marker:
...and there ya go. I had a bit left over from a 50-lb. bag after doing two buckets, so I sealed it with the food saver - we'll put this in the pantry and use it in the immediate future:
. How long, do you think, that the flour can stay good for?
Generally, wheat flour has a shorter shelf life than white flour - in a jar in your pantry, you're looking at 6 months to a year. 
Have you visited 
Good tip, Urban. I'll do that next time. Now that I'm thinking about it, I might even seal up individual packages with 3 or 4 absorbers each in them - that way I could just keep "single-use packets" on the shelf in the pantry to throw in each bucket as I pack them, and I wouldn't have to worry about exposing the other absorbers...
