I use a backpack I got from old navy almost 20yrs ago. It’s a canvas style and super comfy... however my best discovery was last year when I took my son to his first gen con and he wanted to carry bags...lol.

I use a backpack from KR Multicase. I like the way it can be expanded to haul two of their full size cases or keep it smaller for one case. Large side pockets. Definitely happy with it as a pack AND the miniature storage system.  Without the miniature cases, it has a lot of room. I filled it several times last year... 
 

I've got 25+ Gen Cons under my belt, and I keep downsizing my pack as often as possible. I've been using a Mountainsmith Blaze, OOP.  But they offer other packs in a 10L or 13L size. It's a shoulder bag that holds 2 water bottles, charging cable, battery, food, and pens. Best part is if it gets too heavy with "stuff" it turns into a great waist pack.

www mountainsmith dot com 

The north face borealis.

It is a great general backpack, and the laptop sleeve inside is the perfect size for game manuals and sheets, so it doesn't get scratched or crushed. Great breathability on the straps, and it is pretty water resistant (I use it in the rain a lot and haven't had any wetness.  
​​​​​​
downside? It is a $100 backpack, but guaranteed for life.

The best backpack by far is “The Ultimate Boardgames Backpack”. But if you don’t want to spend almost $200 than at least make sure it has padded shoulder straps, padded back and if you carry a beverage, make sure it has an outer side compartment or mesh you can put it in. The Ultimate Backpack has built in cozies. It also folds down to be airport carry on size. 

For something casual, Eastpak Canvas or Topman are both super hot right now. I usually stick to the tried-and-tested brands for bags, myself - Herschel, Sandqvist, Ally Capellino. You may also consider a smart backpack, they are a little flavor-of-the-month-y for me. Zara is the lesser bourgeois of the bunch. And for some reason, Fjallraven is still popular for all the wrong reasons.

I recommend a large sack.
One you can only get from a "right jolly old elf".
Not sure what company that is but it's north somewhere, probably Alaska.

It is a Type XXV bag of holding, and will hold lots of games, toys, and coal. 

It's endorsed by elves but not dwarves.

Yes...Gen Con is coming soon and I'm starting to become punchy.

Mike Boozer
Customer Service & Event Team Manager
Gen Con LLC...and a believer!
 

Quecha Hiking Backpack -- This pack is really great.  And at $25 it's far and away the most economical pack I've seen around.

Orc-made sacks get the job done, but boy, are they uuuugly. 

I have a BRPD satchel I use, pretty nifty to carry around water/notebooks/pens/dice and an item or two (pending size) from dealers hall. It's nice and relatively compact making it easy to navigate through crows and lightweight.

The crows at GenCon at the worst.

I use this one: Targus 16” Checkpoint-Friendly Air Traveler Backpack MODEL NUMBER: TBB012US

For daily use it carries two laptops in the rearmost section, up to three 1.5 liter bottles of water in the next section, numerous power adapters, pens, hard drives etc. in the smaller sections. There is more room should I need it and still has two external mesh pockets on the side. Very sturdy with good padding in the straps and against the spine. 

Check out Geek On. They have the Ultimate Boardgame Backpack. It is literally called that. I love it. It evens expands for when I get buy crazy. So yes, Everyday of the Con!!

Get a small backpack.  I know this sounds counter-intuitive, but hear me out.  Get a bag that will hold your dice, a water bottle, and a source book or two comfortably.  Don't put any remotely heavy purchase in your backpack.  my general rule is that when I leave the vendor hall, i go to my hotel first to drop everything off.  Its much nicer to walk around with just a light backpack that you can throw the odd book or dice set into, rather than a big camping backpack full to the brim with board games.  Even if it takes some time from your day.

Obviously, it will depend on what you are doing.  But, planning to carry a large pack for the whole day is a recipe for unhappiness, in my opinion.