Many card shows allow backpacks, but rules vary by venue, security policy, crowd size, and event type. Check the official source linked from the events calendar before packing binders, cases, snacks, or supplies. Some venues restrict bag size, require clear bags, inspect bags at entry, or prohibit outside food. A small local shop trade night is usually more flexible than a large convention center show, but you should not discover the rule at the door.
Pack lightly and keep valuables controlled. Use a backpack for supplies, water, and lower-value binders, but keep expensive cards in a secure case that stays with you. The first card show prep guide and card show etiquette guide cover practical floor behavior. Avoid setting bags behind chairs or under tables where they can be forgotten or moved. If the show does not allow your bag, nearby card shops or your vehicle are not secure storage plans for valuable cards, so adjust before you travel.