These change based on the type of venue you're at, how long you're in line, and the weather!

• A good camera. Even if you don't want to spend your time recording, it's still an essential to get a few good clips or shots! Sometimes phone cameras can do this, especially if you're short range... But if you're back row or even a medium distance from the artist, a good camera is a great investment! My current fav is the Canon SX740 HS! It has amazing zooming features and it retains quality. I was nowhere near Olivia Rodrigo yet my photos look like I was standing right in front of her!
• SUNSCREEN! It's not necessary if you're in an enclosed venue and you're never waiting outside in lines, but if you plan on camping for barricade or you're at an open stadium or ampitheatre, pack that sunscreen! I've never been told to throw away my sunscreen, but if you're afraid, get a travel-size tube you can part with after using!
• POCKETS / BAG! Typically, I try to travel without a bag as often as I can. It's rare, but I've been to venues that make people with bags stand in a different line so it takes longer to get into the venue. If you're not rushing for barricade, this isn't a worry. But I'm impatient and I wanted merch, sooo.... I ditched my bag with my dad. Also, check your venue's website to see what their bag policy is! Some venues are bag friendly, some aren't. Some have strict rules, like based on sizing or whether your bag is clear! Rather than keeping up with these rules, I typically just downsize what I'm bringing and try to wear pockets that can fit my items.
• For payment method, I suggest a CARD! I've been to few venues that actually accept cash. It's likely in your best interest to bring a card! I always carry a little cash, but I can't recall ever being able to use it. Though I'm traumatized by how many times I've gone shopping and they've told me, last minute, they don't accept card, and I've had to pray that I had enough cash. Sooo I always carry. Even if it's just $20.
• GOOD FOOTWEAR! This goes back to venue, waiting, weather, etc... If you're waiting in lines for hours, have someone nearby that can bring you shoes for the conert if you have some cute, uncomfortable shoes you'd like to change into. But don't risk your foot health in the meantime! Nothing kills my vibe like realizing every step hurts so bad that I can't even dance along to my favorite songs! I've stopped wearing uncomfortable shoes to concerts and I typically go in hey dudes (not the cutest, but it's worth it if I'm walking half a mile back to my hotel!) All of this to say.. if you're short and on the floor or pit, heels are a good choice or you may not be able to see!
• Water!Bring water if you're waiting in line! It gets hot and not every venue will provide any sort of refreshment, which sucks in places like where I'm from. You'll have to throw your water away when you enter the venue, so make sure you're prepared to buy water inside, too! Unfortunately, I've paid typically $10 for a liter bottle of water that gets poured in a giant cup, without a lid, that I have to try not to spill.