how many neon tetras can you put a 2.65 gallon tank?

none, neon tetras should have a 10gallon. I am not sure what were the people at your pet store smoking, even petsmart tags say 10g + for neon tetras. Also neons are a scholing fish and they need to be in a school of 6 and more. I really wish the tank manufacturers wouldnt put such misleading info on the box :/

You could put a betta in that tank, or some shrimp and snail.

I have 7 neons in a 10 gallon and it seems just right, they are loving all that space just for them :)

None. The only thing you can put in a 2.5 gallon tank is a betta if you have a filter and heater, but even then it's a squeeze. If you put neon tetras in there I promise all you will have is a bunch of dead fish. Ten gallons is the minimum for neon tetras, and you need a school of at least six.

zero, neon tetras are extremely active fish, also they need to be kept in a group of atleast 6 and they need plenty of swimming room (15 gal being a minimum for them), dont trust what it says on the box, the problem about manufacturers is they want to get their junk sold, they dont care if your fish will go belly up the very next day

You cant. They are schooling fish and that means you need 5+ or else they would get stressed out and be more open to diseases and parasites. If kept in groups they will produce brighter colors, be happier, and be more active. They need 10 gallons at minimum. My opinion. Get a betta but research before you buy them. (If your tank has a filter and heater) Good luck though.

Absolutely none. No fish can survive in that 'tank'.