You're going to a concert...what do you wear?

The jeans, and boots or heels are good. Just change out the flannel shirt for something nicer. The flowy shirt suggested above would be good. Or any other cute top.

If they are together at the same venue then wear whatever you're more comfortable in. It's a very wierd mashup of singers so your outfit could swing either way. Go plaid shirt if you're more country. You're in a sea of people I don't think you need to change for the artists style no one can see you in the dark.

I would wear jeans, boots, tank or t-shirt, and a non-flannel over-shirt, maybe chambray. (and I'd also take a hoodie, because that's the way I roll)

On the whole the concerts I go to are very casual.

Nothing to add, just HAVE FUN!!

In the US, pumps=heels!
In the U.K. pumps = sneakers or tennis shoes:)

I always wear jeans and t-shirt or tunic when I go to a concert.  If I have a t-shirt for that artist, I will wear it, if not, I usually just wear a tunic.
I've seen Luke Bryan 3 times - he puts on a great show - people wear jeans and boots and just a nice casual top or t-shirt.

Jeans, a t-shirt and comfortable shoes because I won't be sitting down much.

Have fun!

I'm not getting why the nicer side of casual part? Jake Owen, we have seen several times. He is Very laid back, and very casual. I would assume the same with pitbull, except trashier. ha. Jeans and a nice top or tshirt is perfectly fine. No matter where you are sitting.

Jeans, t-shirt and comfy shoes. It's a concert and you should be able to dance and move.

I still go to concerts for my favorite artists which are Marillion, Tori Amos and classically trained pianist Ludovico Einaudi who's music is difficult to classify. For each I dress differently depending on the venue.

Einaudi usually plays at the Warner Theater in Washington DC and it's an upscale place and crowd. Women are dressed up in black dresses and pearls (of course not everyone, but you get the idea) and men wear suits. So I dress up. They dress like they are seeing a classical concert. 

Marillion always plays at the 9:30 Club in DC which I love because there are no assigned seats so I get a chance for a great spot. It's crowded because it's a small venue (another plus-it's a small venue) and you stand through the whole show. So number #1 for me is comfortable foot wear. I wear my Dansko Clogs, dark wash jeans and a black t-shirt. Lots of people wear their Marillion T-shirts from previous concerts. 

Tori Amos plays in different venues but it's always a huge concert arena. These are assigned seats so I know I'll be sitting through the show. For these I'll wear something between the first two above. Dark jeans, a nicer shirt than the black shirt above and nicer shoes than the Dansko clogs since I'll be sitting through the show. 

Hope that helps a bit. This is just how I've done it. I usually go once a year but it really depends on who's in town when. This past year all three were in town so I went to 3 concerts.