Eyeing this bag on Amazon, seems like a good deal for a quality bag -  SOG Bag

I do not prep much, but figured now is as good a time as any.

Help me fill this bag.  What works, what doesn't, absolute essentials, etc. etc.

I live in Michigan so if you have items that would help depending on location, that would be awesome.

Drago

I carry it every work day and it is tough. Hard rains didn't go through and saturate anything inside. I have owned it for about 2-3 years.

Don’t sweat the fact you’re just starting out, everyone started someplace.  I think you would be better off deciding what you want to carry and then buying a bag it all fits in rather than buying a bag and then deciding what you want to carry.  Are you really going to leave some critical piece of gear home just because it doesn’t fit in the bag you bought?

Objective specific.

Where you bugging to? A mile away in a hill? 20 miles away outside town? Is there water there?

That said:
-Gauze, 4" 12ft sealed
-2MREs
-bag of rice 2lb
-USGI canteen with steel canteen cup
-matches
-magnifying glass (strong)
-bic lighter
-large garbage bag, yes really these things retain a ton of heat.
-machete for lumber, fuel and shelter building
-water bladder 80oz
-mini fishing kit
-Suunto Clipper compass
-Cold Steel SRK
-ultra light sleeping bag (cept your in a cold area so maybe not so ultra light)
-Snare cable or Paracord
-T shirt x2 (added warmth under your current clothes if needed)

I also recommend varmint hunting ammo of some kind, of course 22lr is legendary for this task

What kind of situations are you preparing for?
What kind of terrain/conditions do you expect?
What skills do you have? (can make a BIG difference in what gear you need)

Things you'll want to cover:
Shelter (includes clothing)
Water
Food
Medical
Signaling/communication
Tools
Money (handy for pre-apocalypse problems!)
Defense

Way too small, especially in Michigan. Can't even fit a sleeping bag or cold weather gear in there.
Go much bigger.

Okay, my first reply failed, lets try this again.

If you are going to be carrying this bag with you frequently, you may want to consider something that doesn't scream "tactical," with MOLLE, patches, etc.   Why let the less prepared know you may have essential supplies with you, in the even the flag goes up.  Go gray, and find a less conspicuous, covert type bag.  I really like 5.11's line of COVRT Back packs.  A little pricey, but you get all the cool tactical elements, while still remaining under the radar.

COVRT

Stop, stop, wait, hold up.

Before you buy anything, including a bag, what are you trying to accomplish? Trying to get home from work? Going from your house to another location? Leaving your house to go live in the woods? How far will you need to travel? What type of terrain? Is it urban?

Use some type of process to decide what needs to go in your bag. Filling it up with junk people on the internet said you need is a terrible plan.

I totally agree.
I would also ask how much field time you have had and in what terrain and well as what type of weather?
All of this needs to be considered before you start buying stuff.

If stay clear of polyester.
Get cordura much sturdier.

Prep for the most likely first, least likely last.  Start with a list of your most likely scenarios. Natural disaster, like tornado, hurricane, fire, flood, ice storm, blizzard...  

Then work your way down the list making your bag applicable to handle these situations.  

I have been of the prepping and survivalist mindset for decades and I still don't have a go into the woods and survive BOB.  Not realistic in my AO.  

I have a bag that I an grab in a disaster situation and be comfortable at a hotel, family or friends house for a few days.  I could also grab this bag and head to a family or friends house to help them in case of a disaster.  Change of cloths, the basic utilities and survival items, quick easy and go food items.  I keep my bag small and light, realistic.  

The bulk of my preps and survival gear stays at home, I don't have any false perceptions that I can pack it all on my back and go live in the woods, and I would rate my wilderness survival/ bushcraft skills better than most.  I am a successful hunter, I can fish and trap, I can start a bow drill fire during the dry season, and a ferro rod fire in most realistic conditions.  With all that said I still would not head for the woods to survive as a "bug out plan."

Start with a realistic basic plan and move forward with that.

I would have a hard time recommending a specific model, but you can't go wrong with the following brands:

Kelty
Drago
Maxpedition
or Surplus like and Alice pack or converted hellcat.

My BOB is a dry bag with pack straps on it.  I have other bigger better packs that I could drop my dry bag into should the situation call for it, but a basic dry bag works for me.

As the other posters have said, it depends on your goals, terrain/environment, and experience.
If you can give us a better idea of what you are expecting to do, what the area is like, and how much outdoor experience you have, it would help us give better advice.

That said, I'll go with a thought experiment.
Assumptions:
You can keep the bag at home or in a vehicle.
You are reasonably fit.
You dress for the weather.
You need to survive for a couple days off this gear, while walking over light/moderate terrain.

You'll want to have appropriate clothing already (shoes, socks, pants, shirt, hat, gloves, jacket/coat).  If you don't wear clothes that would be okay for hiking, keep a set in a gym bag next to your BOB.

The biggest things you will need to do is regulate temperature, stay hydrated, and potentially create a shelter.  For this, I recommend keeping 2 pairs of socks and underwear in your pack.  Wet/cold feet is bad news to your mobility.  If you can fit it, a base-layer of insulation might be smart, as well.  Next, you'll want a water container and method to purify it.  For a container, you could use a Nalgene or steel bottle.  Alternately, you could use a hydration bladder.  For purification, a good filter (Sawyer mini) or iodine tablets will work.  For shelter, a tarp (or large piece of plastic sheeting) could work.  A sleeping bag and bivy sack are good, but may take up too much space.  Remember to insulate yourself from the ground!  If you don't carry them, a light and some tools would be helpful.  For food, you can use MREs (heavy/bulky), hiking meals (need hot water), Cliff bars, or trail mix.  Don't make this a bulk of your kit.  If talking about 72hrs, you don't really need it, but having some nutrition will help you perform and think better. If your plan includes cooking, I'd recommend the folding Esbit stoves (cheap, small, simple!), some emergency tinder, a lighter, and some stormproof matches.
Keep most of your stuff inside a waterproof bag.  You don't want to go hypothermic because you only had wet clothes and a wet sleeping bag!

Based on the above, and planning for a small pack, I'd recommend these things:

(in a 2gal ziplock)
2x underwear
2x wool/synthetic hiking or boot socks.
base layer bottoms/top

1L Nalgene with nesting metal cup (for heating water)
Iodine tablets
Coffee filter/rubber band (pre-filter "lid" for your Nalgene)
Sawyer Mini Filter

5x7 or 8x10 silnylon tarp or Tyvek
emergency blanket
6x 6ft sections of 550 cord
4x 10ft sections of 550 cord

(depends on weather)
Sleeping bag or jungle blanket
ground pad
bivvy sack

Esbit folding stove
2-6 Esbit tabs
Bic/Scripto lighter
Stormproof matches in waterproof container
4-6 emergency tinder (Cotton balls in vaseline or Coughlan's emergency tinder)

1x Mountain house meal
2x instant oatmeal packs
3x Cliff bars
3x Crystal light single-serve packets
Spoon

1x AA flashlight
Leatherman/Gerber/SOG multi-tool
$100 in small bills
External battery for phone (and cord)