Justin personally recommends all these accessories and uses many of them himself and has been an endorser of D'Addario strings and Planet Waves products since 2015. 

You'll find stuff you just need to get once in a while like lemon oil (for the fretboard), a capo or a strap and also the stuff you'll be getting through regularly like strings and picks.

Advice from Justin on buying strings: Always have at least 2 sets of spare strings that are the same, and when you break one, it's usually better to change them all because unless it was due to string bending of a nut burr, the other strings are probably on the way out and will sound dead compared with the new ones!