Reddit mentions of TOAZOE Leather Hand Grip Strap Compatible with Canon , Fujifilm , Nikon , Sony and more DSLR , Mirrorless Cameras

Get a UV filter for your lens to protect your camera from drunk people fingers.

Learn to shoot with slow shutter speeds combined with low power flash to freeze action. Balance with ISO.

Carry a wide to medium range lens. Groups are hard to shoot when you can't back up in a crowded bar. Aperture in the 3.5 to 4 range to keep everyone in focus, even if the line of people is a little curved.

Plan to shoot both on and off camera flash. Use a cable to trigger the flash if you can. This way you won't have to concern yourself with flash synch and you can hang the flash around your neck when you need to use a hand.

If the club has low ceilings that aren't blacked out, bounce flash is a great way to shoot. Makes things easy and looks great, and allows you to leave the flash on the hot-shoe.

Smile a lot. Have some cards handy that explain who you are and why you're shooting there. It's generally too loud in a club to tell everyone what you're doing every three minutes, but everyone is going to ask the same question.

You can get a box of 1000 cards from Office Depot or Kinkos really cheap. They don't need to be fancy... just explain who your are and your affiliation with the club and whatever other relevant information.

Arrive early. Make yourself known to the DJ, the bouncers and the people behind the bar.... make friends. Ask the bar owner to introduce you, so that everyone knows you're legit, and maybe you can get soda/water for free. A drink or two, to loosen up might be OK, but don't get in the habit of drinking while you're shooting. Something or someone will just get fucked up.

Be very aware of assholes that don't want you to look at much less photograph their girlfriend. There's always at least one of these guys... and he's likely to get angry if he's had a few to drink.

Gauge people's behavior before you photograph them. If they get upset post photo-taking, just let them see you delete the image right then and there. It's not worth the hassle to keep even one good photo.

Carry spare clothes, maybe some wipes and whatnot... sooner or later someone is going to spill their drink on you.

I shot clubs for about 3 years... mostly the summer months. Had a blast, and damn I learned a lot about how to operate my camera. It's a crash course. You have to be super careful though. Alcohol brings out the worst in some people.

....and oh yeah, don't get ganked in the parking lot/garage making it back to your car. Everyone and their brother and their brother's dog has seen you walking around with a couple $G's worth of camera gear around your neck... probably trade that for a lot of Crack Cocaine. Those people are out there.

One of these things is awesome for when you can't really LET-GO of your camera but need to stretch your fingers, rest your hand...

https://www.amazon.com/Prost-Leather-Strap-Canon-Olympus/dp/B010WMJ9TI/ref=sr_1_3?ie=UTF8&qid=1467482374&sr=8-3&keywords=camera+hand+strap

Commenting to confirm that the Sigma is a great option! Make sure you get the version that has image stabilization. It's easily worth the extra $100.

A nice and cheap accessory is a simple wrist strap. It's great for a light setup and really freeing. No need to go expensive, Amazon has ~$10 ones. https://www.amazon.com/dp/B010WMJ9TI/

Totally. Also I saw some recommend a camera hand strap to put over the laces. Something like this:

https://www.amazon.com/dp/B010WMJ9TI/r

I haven’t tried it, but looks like it can make a difference. For me, split laces like the ones I recommended go a long way making it better already.