Money: take travellers cheques or cash (sterling was fine) - you can't use ATMs - and about £400-450 per person would be comfortable for the trip inculding a decent tip for the tour leader. Change it at the airport (and there is another opportunity about 3 days later at Agra). We usually went on a game drive (or to see the Taj) really early then had breakfast (included) as brunch, so only needed to pay for one more meal - and since the hotels were in the middle of nowhere that meant eating together in the hotel (where the food was generally good). No sites on this trip charged for a camera (but some charged for a video recorder). There is almost no chance to shop - a small shop by the hotel at Ranthanbore, a couple of pricey places in Agra and a pricey art gallery and a souvenir shop at Kanha - so even if you want to buy souvenirs, you won't end up spending much.
Days 5 and 15 - you don't really have a whole afternoon for sightseeing given the other constraints of the day so don't plan on doing any sightseeing on your won.
Optional trips: there was no opportunity to do the elephant rides/tiger shows when we there (which was a shame); it is worth budgeting to do most or all of the optional safaris to maximise your chances of good tiger sightings; Ranthanbore and Kanha Forts were both worth visiting (they are very different from each other, and from the forts at Delhi and Agra
Packing: there is a pool at the hotel at Ranthanbore (sadly nowhere else) so take a swimming costume.
I got through about 6 books in total - there's quite a lot of time on buses and trains, and waiting at stations, plus between brunch and going on the afternoon game drive you usually have about 4 hours to snooze or read.
No point in taking a water bottle despite what the trip notes say - you can't refill it unless you have your own tablets or filter - you have to buy bottled water (which you can do at all the hotels and on some of the buses, so it is not a problem).
No need to take neutral coloured clothing unless you happen to have some- most other people don't, so any attempt to blend in is wasted - and to be honest the tigers and other wildlife are accustomed to this.
No need for women to cover up, except for warmth on early morning game drives (when long trousers, at least 1 fleece and a hat and gloves are recommended), and possibly on trains to fit in with local customs. Covering your shoulders is not a problem but it is simply too hot most of the time not to wear shorts and short sleeved tops. Certainly no need to cover up in game parks, at the Taj or other tourist sites, or in the hotels.
Although it's worth taking immodium, and something a bit less fierce (Superdrug do some nice calming tablets!), and rehydration stuff in case the worst happens - you don't want to miss out on game drives or the other sights, after all - most people on our trip were either not ill at all or only had an upset stomach for a day or so. Take a scarf or something else that you can use to cover your mouth and nose from time to time on the game drives - it can get unpleasantly dusty when there are lots of jeeps hurtling around. I had a tubular cotton scarf, which was perfect as I could also use it cover up my hair when we rattling along in the jeep, and it was light to pack. I've seen them in packs of 3 for about £6 by the tills at TKMaxx (called a comfy) or you can order fancier ones from National Geographic (called a buff).