Good advice Larry!
I used to say similar to people in the shop ... Even with things as simple as batteries! People would often want to buy a second one, my recomendation was alway the same - come back and buy a second one when you find the first is running low on you between possible charges.
Same goes for all other kit as Larry says ... People often wish they had more zoom or wider angle but in reality will very rarely use those lenses ...
The only thing that I would say that sorta goes against this advice is again somthing I would suggest to customers when inwas asked what would make a good second lens! Instead of buying a lens that will seemingly limit you less ie a tele or wide zoom. Buy a lens that in some ways will limit you more ie a prime lens!
Nikon make a 35mm 1.8 afs, that would be the obvious choice for a second lens IMO!
What a lens like that does is takes away the ability to zoom, you are forces to frame with a fixed field of view.
Your compositional skills will improve a lot quicker this way ... The added bonus is that it is a lot better for takin low light photos and can offer a nice shallow depth of field