At least a momentary switch., most people would probably recommend a master on/off switch too.
Maybe more, but more info is needed on what you're trying to do. I'm going to assume you're using a Li-Ion batt @ 3.7V (protection is always recommended).
If you're using a
single 3.7V batt, or multiple 3.7V batts in a
parallel config, then there is nothing else NEEDED, unless you WANT to add an led.
If you're using 2- 3.7V batts in
series then you probably want to use a 5V regulator.
If you're using NiMh rechargables then you'll need at least 3, probably 4 in series to get a good
vape (
see the puck how-to).
If you look
through some of the sticky's there's some good how-to's to give you an idea what's needed for your setup, or with more info on what you're doing someone here can probably tell you.