Here is of list of items that you may or may not need during and after your build. Extra things like screws, standoffs, lipo bags etc.
This is the RioRand LiPO checker. It allows you to check each individual cell to see if it may be damaged or over drained. it plugs straight into you balance port on your battery. It has a built in buzzer and is small enough you can plug it in and mount it for a easy low voltage alarm for your craft.
This Abaige RC LiPO battery bag. is lipo safe for storing and charging your LiPOs, its hold up to 6 batteries and it fits in my backpack pretty well.
The Vicdozia 2.5mm lens. is the one i ordered but you can get any brand. Just make sure it fits your camera the standard lens that comes with most cams is 2.8mm the 2.5mm is a wider angle allowing you to have a larger Field Of View.
I got the NALAKUVARA 300pcs. To have a variety of nylon standoffs on hand. never know the setup you gonna try to build and you don't want to be limited, because you don't have to right standoffs. Again this is what i ordered mainly because of the shipping ETA. Im sure there are many other good options out there totally up to you.
I ordered the 270 pc HNBR O-Ring set. Just to have a number of small o rings on hand, they have cam in handy soft mounting my boards, also on some props i got i ran out of threads on my motor before the nut tightened all the way up to the props, a o ring between the nut and prop was a perfect solution. Again im sure there are many other o ring suppliers, i chose this one for ETA shipping, Also im sure if you already have a set of o-rings around the house youll be fine.