It depends how long I'm going to be gone. If I'm just out and about for the day, I usually keep one or two extra fully charged batteries on me (depending how fresh the one in my zmax is) and at least two full cartotanks. Never really saw the need for much more than that if I'm not going to be out for more than a day.
If I'm going to be gone overnight, I keep an extra battery or two on me, my charger, a few egos, my cartotanks, a few spare cartos, and whatever juice I'm vaping on at the time.
Q-tips, vapertowel, etc are just standard.