Whereabouts is the hotel that you are staying and have a pre-booked taxi? Are you in Nice itself or somewhere further away?

One option will be to change the taxi to collect you from the hotel later in the day so you aren’t sat waiting at the airport for ages. Check-out your hotel at 10am, leave luggage at the hotel, enjoy your day and then head to the airport in time to grab some dinner there. Without knowing the details of where you’re staying this is probably the simplest thing to do.

If you get dropped at the airport with your luggage after checking out of your hotel at 10am you may find that you can’t check in your luggage in until a couple of hours before the flight, in which case you can pay to leave your luggage at the left luggage at the airport (terminal 2, call airport to check if it’s currently open before making a plan that relies on being able to use the left luggage).

Nice airport is on the tram network and if you do end up getting there very early and using left luggage you can go out to the local area quite easily. For example Parc Phœnix is very close to the airport by tram. It is a paid entry garden with some animals and you could spend a couple of hours there. I don’t recommend it as a tourist attraction to make a special trip to, but if you’re stuck at the airport area it is better than sitting in the terminal. There’s even an egg hunt for kids on East Monday. Parc Phœnix