Be sure to check the venue's site/etc for bag rules - went to a concert last month at an venue I've been to like a dozen times before with some friends and they weren't letting anyone in who had a bag bigger than like 6 inches & they had to be clear. (which pissed off one of my friends who'd brought like a canvas bag specifically for carrying the blanket she was gonna put out & they refused to let her bring it inside even after showing it only held a blanket)

Be prepared to be gouged for anything food/drink wise. I spent $13.00 on a $5 can of liquid death (which my high ass was initially like 'wtf this is a fucking seltzer i asked for water dude' to the poor teenager working lol) and a $7.00 soft pretzel. If you're gonna get wasted, I'd probably recommend pre-gaming outside but I've had luck bringing airplane bottles of liquor in my pockets (and had friends who would put them in their bra) and buying a 'cheaper' soda to mix/chase it with. If it's outdoors, you can probably get away with sneaking a joint in (especially if you smoke cigarettes) as most places aren't gonna care. If you have an electronic vape/cart for weed, same thing and even easier in most cases.

If it's packed and you've brought like a blanket/chair/etc - do NOT be afraid to strike up a conversation with a couple or stranger who might be using way too much space and ask them if they mind if you park right next to them. I have a friend who is a fucking master at this and always leaves concerts with like one new 'friend' they've made in securing us a spot; never takes her more than a 'hey do you mind if we/I put our stuff right here?' and a 'excited for the show?'. I personally am a bit too self-conscious to ever do it when its really packed, but if you just don't want to be standing behind a pillar or something and see a spot you could theoretically stand/sit in if someone is gracious enough to pull their chairs together or step slightly closer to their group - it is always worth doing. A large chunk of people who get like lawn chairs and whatnot at concerts are perfectly fine with giving up a bit of space to let someone squeeze in, as long as you're not rolling like 10 people deep with three blankets or something.

Merch for bigger shows usually sells out by the middle of the concert, so if you're dead set on getting a poster or something, be sure to stop when you're entering the venue or, if they play a song you dislike/don't care about early on, step away at some point during the concert early. As always, the really dedicated people will be at the merch booth as soon as the venue opens and will wait in line while the show is happening - so bear in mind that you may never get that really cool piece of merch if you wait too long, but eh.

Bathrooms will always have a line, but less so when the show is on - so like merch, I usually try to time this for songs that I dislike or have heard live way too many times before. Depending on the venue though, you may be able to hear the show without issue while in line for merch/bathroom/etc - but it's always a bummer being next in line for the bathroom and hearing your favorite song start!!!

All in all, I actually prefer going to concerts alone because I can just stand/sit somewhere and not really have to worry about my friends (who love dancing) & do stuff like spend 30 minutes in the merch line as soon as the venue opens or sit down and vibe the entire concert - so have fun!!