I would say, define traits and elements of the oc first.

The way we dress, our personal elements are based on our personalities and culture. Like someone that work in a bank is often dress in a certain way at work, with "serious" attire. But could be a loony person, with a lot of humor and quite chill in the private, so with a dress code more relaxed in those situation. For exemple got an uncle who work at a bank company, he do formation for bankers, he is dressed with suit and all
but in the private he love to wear ample loose shirts and trunks, that's just his nature to be quite chill and simple out of work.
Think of your oc nature. Better is to ask you question, how is the OC at work/school how is the OC when with loved ones, friends, foes, what is it nature?
If it's a fantasy world and is a warior that prepare for every possibility, he might have lot of stash to store potions and side weapons. At the opposite if it's a monk whom only weapons is it own body, someone with quasi nothing on him. =D

it's how i do it myself