I CANNOT believe that no one has started a "Bag of Holding" thread yet....

List away

Here's mine.  My pack is just a regular North Face bookbag type thing like you'd see in school.  Nothing fancy, nothing rolling.

• Dice
  
• Pens (several)
  
• Mechanical pencils (several, all full of lead and good erasers)
  
• Wooden pencils (several, as loaners)
  
• Pad of paper
  
• Pad of post-it notes
  
• Snacks *
  
• First aid stuff **
  
• Water bottle (insulated, so it won't sweat all over game components)
  
• Insulated coffee mug (with a leakproof lid)
  
• Electrolyte tablets
  
• A folded up reusable grocery bag in case I buy a lot of stuff
  

** I bring a few band aids, some headache relief of choice (I use tylenol), and some tummy remedies.  I bring Pepto tablets and Tums.

I used to bring a ton of rulebooks, graph paper, etc. but found I never used the stuff. 
 

I have a standard backpack, in which I carry:

• Any books I need for the day
  
• My adventure binder(s) (for games I'm running)
  
• My player character binder (for games I'm playing in)
  
• Pencils
  
• Dice bag
  

I have a small North Face sling bag with a lot of little pockets.  I usually carry:
Copy of Savage Worlds adventure edition or similar small-sized RPG
deck of cards
Dice bag
Otterbox with a few miniatures
ipad mini
a couple of Quest bars

For a day at Gen Con, I'll throw the small bag in a larger backpack with a bottle of water, reMarkable tablet, and room for some larger books.

I have my backpack and TWO (yes, two) Fanny packs.
Among the thing I carry include, but aren't limited to:
-Laptop (you never know when you need it, I had to use it twice on the floor before)
-Tablet (PDFs of RPG books)
-Dice bag (with my D&D dice)
-Bag of pencils and pens
-Trade Binder (TCG deals happen)
-Deck Boxes with decks
-Snacks (mostly fiber stuff so the insides don't get bad)
-Aspirin, Cough Drops, and Bandages.
-Chap Stick
-Power Banks and Cables for them.
​​​-Duct Tape (again, you never know)

I know I have more on me, but you get the idea.

I happen to know someone who will be selling pens and pencils just in case y’all run out

I use a mini backpack and try to travel light.

* A water bottle in a side pocket
* Snacks for the day
* A mini "first aid" kid with a couple band-aids, moleskin, ibuprofen, and antacids
* Hand sanitizer
* An extra face mask (probably bring one even if not required, just in case)
* Small notebook and pen
* Power bank + cable for my phone
* A set of dice
* Folded up large shopping bag to consolidate small vendor hall purchases
* My white cane in the other side pocket, for the times I need it
 

I try to travel light, so I use my badge holder to carry as much as possible without cutting into my neck

• Small pad of notepaper, usually from the hotel
  
• Pen/Pencil
  
• Tickets for the day's events
  
• A few generics, in case something comes up or someone else needs them
  
• Mini-pack of Tylenol/Aspirin/Whatever, just in case
  

Different approach if I'm planning to hit the Hall Of Wallet Emptying; Then I take a backpack.

Boring answer, but true:  NOTHING  (badge, wallet, today's tickets, no bag at all)

One of the main reasons that skyway or close downtown rooms are so desirable is so that you don't have to lug around all this stuff.

If I am forced to carry a day pack due to needing a PHB, character sheets, dice then I probably have a longer event and I'll likely add a beverage + small snack like a breakfast bar or banana and maybe a portable battery. But, even then, it is prudent to keep down weight as much as possible.

I'm usually still shocked when I see people lugging around these huge backpacks all day.  That seems unpleasant.  I guess they're young than me.  But it ain't good.

Back in 2019 I brought a backpack, which was overkill for what I was carrying in, but great for any loot I was carrying out. Inside was A) a pencil case with some dice and writing utensils, B) assorted OTC medicines (light painkillers and stomach stuff), C) about 4 cans of soda, and D) snacks. 

I didn't need more than that, but seeing people's responses definitely has me considering some upgrades, like the power pack and some more first aid supplies. Should probably also add hand sanitizer to the list.

Pathfinder & D&D stuff
dice, pencils, and other gaming necessities
Magic decks
Snacks
Plenty of clothes
Deodorant and other hygiene products, a must have for everyone else's bags
Advil

My 'everyday carry' is:
a small notebook
2 pens
2 mechanical pencils
Medical Tin: Altiods box with a few band-aids, 2 travel packs of tylenol & aleve, a few pepto pills, & a dose of Imodium. 
A drink of some kind that becomes a water bottle as the day goes on.
Belvita breakfast crackers / Captain's wafers
a couple mini candy bars
a small card case for promo cards
a small cardboard box for mini-fig/dice purchases

I'm kind of curious about the number of people who specifically mentioned they bring bandages/band-aids....have people been finding themselves in situations at Gencon where band-aids are needed on short notice? Or do folks all just carry bandages on a regular basis anyway?

* I mean I carry it with me in everyday life 

I largely agree with Matthias9's point that the appeal of a nearby room is precisely that you can leave your stuff there and not worry about it!  It is a little hypocritical for me to say that, though, since most years for the last decade I have left my stuff in the Auction backstage area since I am a volunteer there, and that is even closer than the room, haha.  I am looking forward to seeing whether I can stand to just literally come to the convention center every day with just my badge and wallet!  Probably not, particularly since if nothing else I will be wearing a badge holder.

The only things I have to contribute not mentioned elsewhere that I have been glad to have on me:

• Black and silver Sharpies, for autographs on light or dark surfaces respectively
  
• Pre-packaged wet wipes of some sort (maybe I am the only one who manages to touch something sticky at random most years, in the fashion that other people manage to need band-aids)\
  
• Tape; I know "duct tape" was mentioned, but I have twice felt like MacGyver just thanks to having a miniature clear tape dispenser on me (like, half the size of your finger small), to say nothing of the handful of times I have used it to affix "do not disturb" signs that do not want to stay on the door handle.
  
• A good insulated sealable cup full of ice from your hotel can be really helpful if you boldly believe you can find water to fill it with (though perhaps less so in the less-guaranteed-scorching September convention)
  
• A poster tube with a carrying strap
  

Mind you, I have not been in the "buying posters at Gen-Con" demographic for years, but the one year I finally carried that allowed me to keep my posters safe, instead of having to immediately and awkwardly walk them back to the hotel room, well, that was very nice.

Also this is hardly something to have in your bag, but I have been increasingly inspired by elaborate cooler setups over the years, particularly after reading the Keeper of Ancient Gen Con Lore's suggestions to bring a prefilled picnic basket with you that is so bursting with things to eat that you could probably survive just on what you have with you if you had to (but of course going out to eat is too fun to ignore).

I was definitely bringing mayonnaise, hot sauce, and Splenda packets with me for a few years since whatever I bought to eat or drink at the convention center always seemed to benefit from at least one of those (I did not find anything that could use all three, sadly).  But I realized just not eating or drinking anything at the convention center was probably the right decision, haha.

A few things (*) I probably won't bring because I mainly use them due to the auction and shipping.

- Snacks (typically granola bar, nuts and tuna/cracker kit)
- 1 or 2 energy drinks
- Headache powder
- power cord/charger
- preprinted address labels (for shipping.. I just slap them on)*
- box tape*
- notebook
- pens
- hard top loaders with penny sleeves (to protect promo cards or sometimes from artists if I get a sketch card)
- book (why?  No idea.. I never read it, but in years past since I was never downtown, I was always WAY early downtown just to make sure I got a good parking spot, but even then, I usually find someone to talk to)

I am excited to learn that headache powder still exists; I only knew it from the interstitial jokes on SiriusXM's 1940s music station, haha.