The amount of kit I like to carry around with me is 3 batteries, 2 atomizers, a small bottle of e-liquid (I'd prefer to carry a smaller bottle just to not carry an unnecessarily large stash of e-liquid, but even a "big" bottle is only 15mL, which isn't huge).
Theoretically, if you used a DSE-901 or one of it's variants, you could fit most of this inside a pack of cigarettes. So far I've lost one DSE-901 (atomizer and battery, just was stupid and lost it somewhere) and killed a RN4072 battery by throwing it in the washer with my clothes, so I strongly recommend some form of carrying case.
Theoretically, if you used a DSE-901 or one of it's variants, you could fit most of this inside a pack of cigarettes. So far I've lost one DSE-901 (atomizer and battery, just was stupid and lost it somewhere) and killed a RN4072 battery by throwing it in the washer with my clothes, so I strongly recommend some form of carrying case.