IMO short on details. There are probably more variations of paan than the number of times Emeril has used the B-word. Every region, possibly city, has its own 'special' type. Very broadly classified there are, as has been mentioned two types – meetha (sweet) and sada (plain). There is also a subtype which could be either sada or meetha – this contains tobacco – zarda paan (now isn't that a chew!). The tobacco itself comes in a variety of types (with saffron, 'sweeteners', spices, etc.) depending how it is perfumed; the term laced may even be appropriate sometimes.
I'll say. There are as many varieties of paan as there are paan-makers,
really

And, as you say, lots of secret recipies.
One particular paanwala in Bombay, for example (sits kitty corner
from Delhi Durbar restaurant in Grant Road - coincidentally a block
away from the "red light" district of the city) is quite famous for
his paans. His most notorious is the "Palang-Tod Paan" (Palang = Bed,
Tod = to break; bed-buster might be the loose translation). This is known
throughout the city as a quite famous aphrodisiac - and is, supposedly,
laced with cocaine-paste.
A lot of paan used to be made at home – I would guess this is a declining practice. I remember seeing the daily ritual of paan making at my grandmother's, starting with slicing the supari (betel nut). The way this is sliced or cut in pieces makes a big (textural) difference. The paan leaves are cut as per the rolling style – there are hundreds of ways paan can be rolled and folded. The leaf is smeared with the pastes as Zim noted and then some spices and flavorings put in. These spices and flavourings (some of which are liquid, think essences) and the combinations are tremendously variable
.
Yep, was a regular thing - grandmothers everywhere, cutting and
slicing their own paan regularly, every day. If you walk up some
apartment buildings in India, the walls are sometimes strained red
head-high - due to the colour of the expectorant thats been spit
on them
(In one of the early Salman Rushdie books - Midnight's Children, I
think it was - there is a famous scene of the game "Hit the Spitoon"
played by elderly men in Delhi. The Indian version of mouth-basketball -
with, supposedly, as much appreciation from onlookers for the trey
as Da Bulls-Fans had for Steve Kerr).
I suppose the answer to your original query about what goes in is that it is too varied.
One can also get the paan filling sans paan – as a kid, I would opt for that (sans supari too; I just liked the sweet filling for the meetha paans – this was, I will note without the rose flavouring, possibly not endemic there). Prepackaged Paan masalas have since become a big commercial enterprise. PanParag is a brand I readily recall, their blue tins are fairly ubiquitous in India (see their product line-up). Some of these are labeled and sold as mouth freshners
http://www.panparag.com/home.php
Paan Parag is hugely popular - ubiqutious among certain people
even in Chicago, who carry it everywhere they go. Can get it
at most Indian grocery stores too, I think.
c8w