what comes in the box? like seriously I'm at a lost for words. You don't really "need" any of these accessories because they are just that. These things will be tuned to whoever they are marketed towards. I'm not going to recommend buying expensive headphones to someone who may or may not listen to a lot of music...seems pretty pointless right? same thing with recommending a case to people who like to use skins or just straight up nude with their phones.
Things I think are nice additions are the following.
1. A dock. A frivolous item sure, your only going to use it when your at home at most likely your desk or office area. I guess it's good for taking with you on trips as it's good to have on your nightstand, but finding uses for it is limited...lets just be real. Your buying a dock cuz you want your phone to look cool.
2. Protection. It could come in the form of a tempered glass screen protector, a skin, or a full on multi-part case. I think apple charges too much for any of their cases but the quality is there for those who care. I think a tempered glass screen protector is a must if your using those thin cases, if you go for an otterbox, your already good.
3. Battery management. Cables, chargers, battery cases and wireless charging and power banks are all thoughts people think of when it comes to this. I personally Think power banks are the better option since you can use that bank to charge more than just your phone, great for ipad users. You should opt out to get a better cord/cable tho. I'm sorry but apple's stock lightning cables suck...
4. Miscellaneous. Headphones, bluetooth speakers, controllers, etc. Do you need something better than those stock ear pods? Well I would suggest researching headphones in your budget that meet your needs. There are better and more affordable headphones than Beats. I personally use Sol Republic's Track HD headphones. Near Indestructible bands, and everything is modular and swap-able. so in the event a driver goes out or my cord gets damaged, I can order new ones without having to buy a new set of headphones.