Today someone asked me what gear do i have, and instead of telling them what i had, i started telling them the essentials, in my own experience. I found some thing to be essential to have in my bag. They are a 24-70, battery grip, speed light, memory card read and finally lens cleaning kit. I'm going to write this in no particular order, as i believe them all to be just as valuable to have on you at any given time during a shoot, so lets get into it.
A Memory card reader, preferably USB 3.0, you know when you want to transfer something but you can't find the lead. That is the reason you need to always have a memory card reader with you. I've had this happen a few times and that would of solved everything.
Battery Grip. This has changed the way i shoot and makes a world of difference whilst on a job. I have the Nikon grip as i had a number of third party ones which all failed on me one way or another. The main reason i like grips is because of the vertical shooting position i am in. It feels so much better when shooting in the portrait position and looks more professional too. You elbow isn't swinging around and hitting people and you are less likely to get knocked while trying to get the crucial shot at a wedding.
24-70...now i know this may seem stupid to some people but having a medium zoom lens in your bag would get you through most situations. It doesn't have to be Nikon or Canon glass either, any third party 24-70 will work as effectively despite the slower focusing and other things that come with third party lens. This is probably by far my most used lens, it was the last one that i purchased for some reason, i bought the 14-24 and 70-200 before this and honestly i don't know how i managed. It such a versatile and sharp lens, definitely my 'go-to' lens.
Len's Cleaning, sometimes you find yourself climbing into bushes or laying down or or a beach. Then if you shoot above F4 the you can see the dirt in your photos... yeah SOO annoying, i have at least one cloth in every bag of mine. You can just get any microfiber cloth and it'll do a great job.
LIGHT!...You have to have at least one speed light in your kit, no matter you shooting style it has many uses. From just filling in some shadows, and quickly and simply setting up a dramatic portrait. You can also use it to balance light which in my opinion makes separates the photographers from the picture takers. Again it doesn't have to be the manufacturers light you can pick up yungnuo very cheap. ( i have recently bought one)